I read somewhere that using your crypto wallet to scan qr code might not be safe, since it's possible to hide links or something bad in these Codes but since my crypto wallet isn't internet 🛜 ready will they be affected?
There are a certain risks, but they are easy to spot and avoid. Scammers can place a fake code over the real one, which would send the funds into a scammers address if you scan and send. But if you intend to spend your coins in a store around you, then i doubt this can happen and if it does, then it ought to be on the merchant. So just verifying the address is enough. And if you scan a qr code and it redirects you to a website or something, it is probably a potential scam.
Assuming I visit a local store in a country where Eth or other coins are acceptable as payment, then instead of using a hot wallet I use a Trezor or a airgapped wallet to scan their QR code, is there any possible threat doing this?
This would require a few steps. I.e. if you are spending from your airgapped wallet, you'd need to scan the qr code with your watch-only wallet and create the tx there, then move it to your airgapped wallet, then sign the tx. And then finally move it back into your internet connected watch-only wallet to broadcast the tx. These steps a lot of people would be unwilling to take just to spend a few $ in a local store. This is why i keep ~ $100 or less in a hot wallet and it is funds for spending on the go. It is easier and safer to do that way, than moving around with your cold storage wallet.