I recently looked into this because of some international travel coming up and Airalo seemed to be the best option. Yes, it's a bit more expensive that buying a physical SIM at your destination and possibly more limited (I did not see service in Ethiopia listed, for example). So I'd start by checking out that app and seeing if the countries you visit are listed.

Also, I don't know where you're located, but where I am at least there are plenty of 13 pro max phones available. That also might be a good option so that you have the SIM tray. It would still be a huge upgrade from the 6 and would last you years. So I'd check around to make sure buying a 13 isn't an option.