Isnt that a root-only app?

Because if it uses the internal VPN feature, EVERY system app can bypass it, and the Captive Portal app and others certainly do.

Only GrapheneOS fixes that afaik, providing their own Servers for captive portal, connectivity check, SUPL proxy server (strips off data and Google still has to manage because monopoly)

There's fork that gets updates

https://github.com/Helium314/openboard

and also has no predictions, which really slows it way down since you have to type out each long word the whole way through instead of just getting it to the point of uniqueness and clicking the suggestion.

Here, its with the secondary functions of letter D, J and N. Yeah no predictions is not a feature but I like to scroll trough text with the space bar and delete backwards. Plus if you hold a key it keeps going like a regular keyboard which I like. Overall I think its a good option for composing emails if you get the hang of it.

This is depending on the OS one is using so I did not mention that it is possible on some operating systems

If you do not have an LSposed framework or similar (formerly knows as Xposed Framework) you can either use Adaway for blocking the phone from reaching websites (keep in mind that this is globally, though) or e.g. AFWall+ for preventing single Apps to connect to the internet (Apps that don't try to get internet access are not shown is the list provided by AFWall+).

If you have LSposed or similar I believe it is possible to install XprivacyLua. This was/is(?) a very powerful tool to manage every single access an app is trying to get. Why would a sketchy chinese calculator app need access to the contacts and the internet even though this was never allowed in the system settings?