[ingenium]

Android is pretty easy, you just add it to the keystore and that's it. I've had my own CA long before Let's Encrypt, but now mostly only use it for non-public devices that can't easily use Let's Encrypt (printers, switches, etc).

[crapple8430]

You can add it to your user CA store, but no app will trust it since it's treated differently from the system CA store, which you can't modify without root or building your own ROM. In effect it is out of reach for most normal users, as well as people using security focused ROMs like Graphene, when ironically it can improve security in transit in many cases.

[noirscape]

It's technically possible to get any Android app to accept user CAs. Unfortunately it requires unpacking it with apktool, adding a networkconfigoverride to the XML assets and pointing the AndroidManifest.xml to use it. Then restitch the APK with apktool, use jarsigner/apksigner and finally use zipalign.

Doesn't need a custom ROM, but it's so goddamn annoying that you might as well not bother. I know how to do these things; most users won't and given the direction the big G is heading in with device freedom, it's not looking all that bright for this approach either.

[ingenium]

I mean it works fine for me on Chrome