a) Google voice doesn't operate outside of the US, and I'm not aware of any equivalent that does, short of setting up, paying for, and managing a full-fledged voip line (e.g. with voip.ms) which are pretty finicky with 2FA codes.

b) These systems are a general pain when you need to deal with human support if your number on file doesn't match the number you call them from. I have a few different numbers that I use variously and run into this every so often - I get a barrage of extra verification questions if I call from a non-matching number, callbacks seem to happen randomly between my number on file vs. my number listed in a ticket, etc. My wife teases me about constantly breaking systems due to hitting untested edge cases.

(Tangentially, various systems will require you to input a phone number with no information stating that it must be a number capable of receiving texts, and at some future date will try to send your landline authentication codes via SMS.)