The multi-sig wallet I use is Sparrow https://sparrowwallet.com/

I don't have signing devices, but I do have computers lying around that I happen to almost never turn on (a laptop with a shot battery is very inconvenient)

I happen to know about a type of malware called a worm, which infects other computers that are connected to the same network. So for this reason, I wanted my multi-sig setup to be such that the number of computers required to spend are first and foremost not connected to the same network at the same time. In particular, my shot battery never connects to the internet

The computer which is connected to the internet, also runs my full node, so when I spend, I'm not trusting someone elses.

I also nerd out about air gaps sometimes: https://cyber.bgu.ac.il/advanced-cyber/airgap

Transmitting the PSBT via QR code is built into Sparrow and I like it. I don't think you can buffer overflow with QR code transmission.