I am in a semi-similar situation and I use an MVNO called Ting. I don't claim it will work in every country, but it works in lots of countries (all that I've tried) to receive 2FA SMS, and costs usually less than 10 bucks a month depending on how much you use it overseas.

My phone number works great for Whatsapp and Telegram. However, the caveat is that they don't currently support e-SIM, so if you have a USA market iPhone 15 (no SIM slot) then you're out of luck with Ting, and presumably future iphones will also not support hard SIM cards. Overseas (at least EU) market iphone 15's mostly seem to have SIM slots still, so maybe that's a workaround.

Furthermore they seem to be mostly honest, let you chat online with an actual English speaking human on relatively short notice, and have a fairly straightforward website without a bunch of dumb interface chrome. Also it's a "real" phone number so it doesn't trigger the VOIP detection filters that sometimes plague you during various signups.

Lastly, I suspect that probably many other MVNO's will offer a similar setup, they're cheap so you can probably A/B/C/D test a handful of them in parallel in whatever subset of countries is relevant to you.