I tried to set up a Google Voice account (even paying), to receive a number where I could get SMS and set that number as my 2FA for those apps.
However, Google Voice is not allowed in my country. Is there any trustworthy alternative that I could use? I think Twilio may provide this service but not sure if I could get a nice dashboard for this (I do not want to code an API).
Just to clarify, my only requirement is to have a SMS number to receive 2FA codes from outdates apps that still use that (also, when travelling abroad would be easier because I wouldn't need roaming, only an internet connection)
This page shows their pricing in various countries (https://voip.ms/business/pricing#improved_communications_con...). For the US the "pay for usage" variant costs $0.85/month for the number itself plus $0.0075 per SMS message (for basic SMS messages).
You can configure the number to return the "out of service tones" if you don't want to use it for calling, but as you do mention "traveling abroad" then with a VOIP number you could send/receive calls from anywhere you had a working internet connection to one of their servers. VOIP.ms works perfectly with Linphone (both Linux desktop and Android app from F-Droid: https://f-droid.org/en/packages/org.linphone/) for calling (at least for phone usage, I've not attempted using Linphone's fancy IM or video calling).
As to whether VOIP.ms is available "in your country" -- I'll have to let you investigate that for yourself.
Just curious, what country?