Quote from: moejoejay on Today at 02:21:35 PM

May an easy example will help to explain this further and to figue out if my assumptions are wrong or not.

I'll make up an example for all 3 scenarios, and I'll rewrite your questions.

Quote from: moejoejay on Today at 07:17:17 AM

1. Withdraw from CHP with Import Private Key in Electrum --> Spent the coins.

Let's say I deposited 0.02347273 BTC to ChipMixer on January 1, 2021. I got a 0.023 BTC voucher. Yesterday, I deposited 0.00482361 BTC to ChipMixer and added my voucher. I withdrew a 0.008 BTC chip, and got a voucher (0.019 BTC) for the rest.
Today, I start up Tails OS (which connects through Tor), import the 0.008 BTC chip in Electrum, and spend the coins. I make sure to spend the full amount, without creating a change address.

Quote from: moejoejay on Today at 07:17:17 AM

2. Withdraw from CHP with ~~Import Private Key in Electrum -->~~ Sweeping in Electrum --> Spent The coins.

I shortened the question a bit: there's no need to import private keys if you're sweeping them.
Tomorrow, I'm going to use my voucher on ChipMixer, and withdraw a 0.002 BTC and 0.004 BTC chip. I take a voucher (0.013 BTC) for the rest.
I import both private keys in my normal installation Electrum (which I already have on my PC). I click Wallet > Private Keys > Sweep, and enter both private keys. After the transaction fee, I receive 0.00599617 BTC on the next unused Bitcoin address in my Electrum wallet. I use the Coins tab, select this input, right-click my mouse and click Spend. I spend 0.00456817 BTC and receive 0.00142685 BTC on a change address. I go to the Addresses tab, and Label the address: "CHANGE from CHIP, do not mix". Then, to avoid sending it accidentally, I click right-mouse and select Freeze.
This is still pretty good, as it won't link any of my Bitcoin addresses on-chain. But the Electrum server I'm connecting to, knows all the addresses in my wallet. If it keeps logs, my anonymity could be compromised.

Quote from: moejoejay on Today at 07:17:17 AM

3. Sweeping directly from CHP to an Wallet --> Spent the coins.

This is basically the scenario (#2) above. The level of anonymity will largely depend on the wallet you use: if you use an Android wallet from your home IP address, it's likely someone can link your addresses together. If you use a web wallet for all your Bitcoin transactions, it's even worse.

I think #1 is the most anonymous method if you're limited to Electrum. You could probably do a bit better if you use your own Bitcoin Core wallet on Tor, but that is more work.