congrats @bestcoin_59 !

It's probably 2nd or 3rd option.

Just download Bitcoin Core and make sure you have an SSD (HDD will also work, but I recommend using SSD) with a capacity of at least 1TB or 2TB ~ currently the Bitcoin network weighs around 700GB (I haven't checked it for a while).

Optionally, you can enable pruning so you don't need to keep the entire blockchain stored and the node will only download and check the recent blocks and delete the old ones, you can set the size manually.

Learn how to use the 2 setup software:

1st device holds the private keys and never connects to the internet,
2nd device broadcasts the raw transaction created on the 1st device

This is the foundation of good security when dealing with Bitcoin. Also never use any device that has been created to be used with crypto, even if they are Bitcoin-only, because they make you stand out. You want a generic laptop, a generic USB, things that don't say you hold any coins. And stop dealing in altcoins, they are fundamentally not safe, stick to BTC and that's it.

What makes you puzzled? I think they mean you can install Electrum and store Electrum's data on USB device they sell. Although Coinomi have mixed reputation since in past,
1. Switched from open source to closed source wallet.
2. There was time interval where they doesn't upgrade their software and active in social media.
3. They send generated seed phrase to google server.

On side note, i just noticed that ebay mentioned 11 sold of those USB have been sold.

3. They send generated seed phrase to google server.

Remember that you can use any USB flash drive as a cold storage method, as long as you correctly follow the recommended security steps, such as having a computer exclusively for this purpose (with TailsOS installed on the device or bootable on the USB), where device1will be offline (only to sign transactions) and device2 will be online and the master public key will be stored on it to monitor and assemble transactions (to transfer to the offline device).

1 - Device1 must have wallets such as Electrum, Sparrow, Bitcoin Core... installed and it must be permanently disconnected from the internet (you can consider removing the network card). Once the device is in air-gapped mode, you can create your wallet, write down the backup wallet, add an encryption passphrase to protect the keystore (Don't confuse this with BIP-39 passphrase or electrum seed extension, where you can optionally enable it as well.) and copy the extended public key to device2 online via QR-Code or USB drive.

2 - Device2 can be used normally and will have the aforementioned wallets installed and transactions will be created through it. You can copy the PSBT via QR-Code or USB Drive (the USB Drive will be for exclusive use for this purpose) to device1 to sign and then, with the transaction signed, return to device2 to transmit the transaction.

add an encryption passphrase to protect the keystore

I recommend that you run a full node such as bitcoin core on the online device to transmit the transactions themselves.

[SecuX is a closed-source hardware wallet, and while they did an 'acceptable' job with W20 and V20 models (it isn't compatible with electrum and other bitcoin clients, hence the 'acceptable'), the company's recent products are crap, and to me, if you're going to use an 'offline' signing device that's closed-source, you're better off setting up cold storage on an old air-gapped deevice with a privacy-focused Linux distro like TailsOS.

Wait, I didn't fully understand your cold storage implementation, but some items weren't very clear:

Do you insert your public key into the online or offline device? Remember that the privkeys must be stored on the offline device, so importing the public key into the offline device is useless, it can remain on the online device to create transactions and sign them on the offline device.

Are steps 3 and 4 being done on the offline device?

Step 5: Oops! Something's wrong here, you disabled your internet connection, does this mean that you're doing both the procedures of creating the transaction, signing and transmitting on the same machine?

Step 6: Why do you need to enter your seed phrase every time you make a transaction?

Step 8: Copy the signed transaction to where? - I see in step 9 you're transferring it back to the same device after rebooting with internet disabled.

This implementation makes no sense. There is still a risk of malware stealing all your coins, since the entire procedure is being done on the same device. If there is malware on that machine, what guarantee is isn't recording everything and waiting for the right moment to steal your funds?

And if you save data in storage, should not forget about the "fragility" of USB as a data carrier. Simply put, it can fail at any time and the data will be lost. Therefore, need to make backups.

There are dozens of methods for key generation (even that doesn't implies software like with dices and so on).
I know that these are not methods for everyone but meanwhile it's something boring that people would just rely in a third part solution WHEN they have already EVERYTHING to be totally indipendent.

follow "glacier protocol" guide for having an explanation on how and what to do for your state-of-the-art cold wallet.
Otherwise you're just getting trouble by buying such items from "random people". If you cannot verify the software / hardware I would definitely avoid any external system. It0s not an option it's a no-no situation

I wouldn't buy it for several reasons besides those mentioned by other members above, for some reason the seller shows Coinomi desktop software, doesn't mention details of the encryption used... just a generic pen-drive like any other.

Never buy products like this, the chances of it being a blatant scam are 99% (very high risk) or someone trying to make a quick buck eBay, even so, would you trust your coins (or your life savings) to a total stranger with a mediocre description?

Buy a Trezor, Bitbox02, Coldcard or Passport (these two are fully air-gapped) and you will at least be following the standard security models of the market.

As mentioned, you can make a bootable pen-drive with TailsOS and electrum built in and have security comparable to a hardware wallet (if you use it offline on an air-gapped device), there are several tutorials out there.

I do not know any wallet for making PSBT but you can use some open source wallet with multiple coin support offline and have the master public key on a watch-only wallet.

I know Unstoppable wallet supports that. Maybe you can try it.

Maybe you can have multiple of the wallet offline so you can just select on one for making transaction if there is any need which will then become online wallet.

Some people just use the method to hold their coins and not spend from it at all.