So, I just learned about this the very, very hard way.
After buying a second hand S10 and finding american ones can't be unlocked, traveling 4 hours to buy another one after much research, much annoyances to unlock it (samsung requires you to be online, which I didn't know) and testing multiple ROMs, I finally read this page more properly https://wiki.lineageos.org/devices/beyond1lte/ which says "known quirks: IMS". I thought it was just something like dolby sound.
What it means is that it doesn't suport VoLTE and most currently used phone systems. Samsung made their proprietary mess, unlike most other developers, which means it will probably never have an open source version.
And that applies to ALL modern samsung phones. I had samsung phone before with a custom OS, but didn't realize because VoLTE wasn't mandatory back then. Now it is here in Australia, and many countries. So if you ever plan to buy a samsung phone to degoogle it, know that it won't make phone calls. SMS and mobile data also doesn't work.
I don't know how I missed this. It should be talked more often given how popular samsung is. There should always be a warning "YOU WON'T BE ABLE TO MAKE PHONE CALLS IN THE FUTURE IF YOU CONTINUE".
S10 was the last decent phone ever made (for me). Not too big, SD card, headphone jack (one of the most important things for me), good camera, etc, etc... That's why I was so persistent to find one to degoogle.
So I'm stuck with my amazingly shitty pixel 5 (and other ones are even worse for me). And considering the possibility of a life without smartphones at all, since this is a losing battle. Mainstream doesn't care and evil companies have every incentive to kill freedom. It has been getting really bad and it will just get worse. But anyway... this post is not about this.
Be warned, if you care about freedom don't ever buy samsung again. Not because they are evil (they are), but because you won't be able to make phone calls on your "phone".
In addition to this, anything on One UI 8 and above does not allow the bootloader to be unlocked, regardless of region. Fortunately, I had already rooted my S23 and have stayed on One UI 7 ever since.
That's good to know. Although that's a more difficult, if not impossible, mistake to make. If you search on installing something different on those phones, as most people will do, they will find that it's impossible before they even start the journey. Buying a phone to degoogle without researching if it's even possible is a bad mistake.
But the older ones it's worse, because not only every research will show it's possible, most reviews I found of the S10 with Lineage were actually very positive, saying everything worked great. Because VoLTE being mandatory is something new, and many countries will still work but not for long.
So it's really bad because if you don't pay attention to the IMS thing you will have no reason to think it won't work. It is possible, it works great, it just doesn't make calls. Silly detail that isn't mentioned well enough.