As for now, when I need to travel to Germany, I just book tickets through the national carrier of my home country, which for cross-border tickets often turns out to actually be cheaper than booking through DB. Thankfully I don't live in Germany proper and my need for travel there is not that high (once or twice a year at most) but I wonder what would I do if I had to move to Germany and use trains there more often.

From what I understand, the problem wasn't with typing characters actually used in the Czech language such as á, ř or ů. The problem was with typing the ˇ character by itself, which is normally encoded in Unicode as U+02C7 (CARON), but there also is a combining version (U+030C, COMBINING CARON), which is what gets printed if there is no precomposed character (e.g. š is both U+0161 and U+0073 U+030C). There is a thing called Unicode normalization that makes "identically looking" strings actually use the same codes, so maybe it was that thing that changed a bit (maybe even somewhere else and not in the lockscreen/keyboard logic), or they could have just removed the ability to type ˇ by itself altogether since it's not something actually used in any language or writing style and most often comes up as a result of a typo.

Since the user doesn't speak Czech, I promptly removed the Czech layout and installed two other layouts, US English and Hebrew, for the languages that the relative uses to type on the computer.

For some reason, login screen just after boot still uses Czech layout, which means Z and Y are swapped and numbers must be typed with Shift (just pressing numbers outputs Czech letters like ěščř). So when booting up the machine (remember that you can't use fingerprint during first unlock), the user must type the password in whatever layout is physically printed on the keys, even though the rest of the OS doesn't even have a mention of that layout. Somehow afterwards the OS "can" see the list of the layouts and lock screen correctly chooses the English US layout.

Alongside of that, for some reason, the key that's supposed to type ` and ~ in the US layout types some nonsense instead (a plus-minus sign and a section sign), whereas the backtick key is for some reason located between left Shift and Z (good luck unlearning years of muscle memory typing ~/Documents in the terminal)

Note that many European countries have already got rid of their 3G networks completely [0]. So it's either "you have 4G/5G" or "the internet is pretty much unusable", nothing in between.

As someone living in a European country with no 3G network, my experience with mobile data is that when my phone fails to find a 4G signal and switches to 2G (pretty much only happens in remote areas, thankfully), I can as well send my packets using a pigeon carrier, they're going to arrive to the destination sooner.

[0] https://en.wikipedia.org/wiki/3G#Phase-out