If you want close to the bare minimum of software needed to run a system, and setup everything exactly as you like it, use arch.

If you want a preconfigured system that is performant, stable, secure, but still able to be customized to your liking, use Fedora.

If your scared of using a comand line for installation, use EndeavorOS.

I have used all 3 of these, in some capacity. I run my servers on Fedora Workstation, because it just works and comes with properly configured sepolicies out of the box. Arch has been the daily driver on my desktop/laptops for almost a decade now, because I often like to experiment with new programs and replacements for commonly used software, and the arch wiki is a wonderful. I tried EndeavorOS on an old PC to play YouTube videos/stream on my TV and it worked fine. I had to uninstall a handful of apps it came preloaded with, but that’s easy enough with an arch base. But IMO, now that the archinstall tool exists and is officially supported, there is actually no reason to use EndeavorOS unless you really don’t want to type a couple commands into a command line.

I don’t have a specific answer, but you could also look for tools that schedule reboots. If I remember correctly, a fresh boot has the same effects as lockdown mode. Fingerprint is not accepted, and the device contents remain encrypted until you unlock the first time.

As others have said, debian is very minimal, so If you would prefer to setup and configure the whole system yourself, debian is a good choice.

Personally, I prefer fedora server. It comes with more things configured out of the box (zram and sysctl configs for example) as well as better security defaults (selinux included with proper policies) and first class support for container infrastructure. Ultimately you could achieve a similar end result with debian, but for my homeservers I prefer to let the fedora team handle most of the system configuration for me.

I don’t know what sponsor you mean, but my Spigen SlimArmor case has little bubbles in the inside of the corner so it can squish more in those areas

For the sake of anyone who finds this looking for a proper answer, SteamOS/Bazzite/ChimeraOS are all suitable for this purpose. I didn’t consider them when writing this because I thought they were primarily game focused, but for non-games like Jellyfin or a web browser, you can just add them to your steam library as non-steam games.

If your doing this on a pi with raspian, both of these packages should be available. You can run sudo apt install cage cog in a terminal to install both of them.

I don’t know of an OS or distro dedicated to this, but it should be pretty easy using cage-kiosk, a window manager that only allows for a single window, and cog, a very basic web app container.

Install cage and cog on whatever distro you want, setup autologin, then in your ~/.profile add something like

cage -- /usr/bin/cog https://example.com

It should boot directly to the webpage at that point. Make sure to set up ssh before you do all this! System management might get tricky if you dont

Android browsers can provide what are called “Custom Tab Intents”, meaning that other apps can request to open web pages in a webview-like custom tab. This depends on browser support, with WebView being the fallback when your default browser does not support it.

If you’re looking for a chromium based browser, I like Cromite (successor to Bromite). Otherwise, Iceraven and Mull are two Firefox forks for Android that work well in my experience.