It goes from 3% slower to 30% faster.
Chances are very high that Kodi will detect your own TV's remote and you can use that! https://kodi.wiki/view/CEC
If that doesn't work, there are many cheap options.
I also use the official JellyFin client on my android phone with MPV as player and that also works perfectly fine. And the Jellyfin Media Player on my laptop is also flawless.
In my experience, the older Chromecasts are probably the only clients with problems.
If I had to buy a client device, I'd probably go with a Minix U22X-J (Max) or Ugoos AM6+ https://discourse.coreelec.org/t/amlogic-ng-and-dolby-vision/24738
I've been using Jellyfin for over 2 years. My main clients are a Raspberry 4 and a Raspberry 5 using Kodi + the Jellyfin plugin. This combo has been flawless.
I also have an older Chromecast and I experience there similar problems with subtitles.
MX Linux is a nice Debian based distro that still supports 32-bit. Or you could use just Debian.
I have spent a lot of time playing GB/GBA games and Advance Wars is among my favorites. I love the "hot potato" mode for playing with a friend with just one device.
Python / FastAPI will be better than Java in your situation and is easy to learn. Go should be even better and is also relatively easy to learn!
I own two Raspberries 1, a Raspberry 4 8GB and a Raspberry 5 8GB. I wouldn't recommend the 4 as a full-fledged desktop replacement, but the 5 has been very smooth so far.
I'm currently using the latest Raspberry Pi OS Lite and installed KDE on top.
I was lucky then with the 4 A400 I'm still using. I also have 3 BX500 that have been very reliable.
LOL! It's a blogging platform called Bear Blog: https://bearblog.dev/