Yeah I'm confused why I get a warning that qr code can not contain all the data of the psbt unsigned tx.
When I scan it on the airgapped machine it gives a warning yellow triangle says cant put the fees and it can be maliciously changed.
I think it's telling you that there is a possibility that someone could change and try to manipulate the transaction. That doesn't mean it will happen. After all, it's you creating it and you broadcasting it afterwards. Why don't you try the entire process with a small amount of a few dollars to see if it will work. Create a $5 BTC transaction on your online machine, bring it over to your airgapped computer for signing, and finally broadcast it on the online computer.
I probably shouldn't use that usb again even though I do format it straight away as soon as I used the psbt from it
Good idea. Use it only as a communication medium between your hot and cold wallet and format it every time on either end if you are worried about catching malware.
Someone suggested to me you can break the unsigned data into parts and make several qr codes but I got lost on his idea.
That's again adding new complexities to the transaction creation process that don't need to be there.