How do I properly replace the stock keyboard app?

In my attempt to de-google my phone, I’ve been using Unexpected Keyboard. It’s amazing and I love it. I’ve used adb to remove the stock google keyboard from my phone and I never ran into any problem until today.

My exams are coming up so I had decided to shift to using a long password to unlock my phone instead of my fingerprint (it helps in significantly reducing my screen time).

It was going well until I restarted my phone and I was fully locked out. The keyboard wouldn’t show up because Android won’t allow you to use any third party keyboard on your lockscreen the first time you boot it up. I genuinely thought that I was fucked and that I’d have to reset my phone to unlock it again. I tried many things for an hour and miraculously using a usb keyboard with an otg cable worked. It was a relief to know that I wouldn’t be losing my photos and documents.

But I don’t like that this even happened.

Like what if this happened when I was outside and I really needed to use my phone? It’d be a disaster. I really don’t want to be forced to keep gboard on my phone and I don’t like the potential risk of being locked out of my phone.

Is there a way to force android to let me use non-stock apps on my lockscreen? Can I somehow turn my non-stock keyboard into a system app? Can I do it without rooting my phone? (I don’t want to do it before the warranty is over).

Think this depends on keyboard eg. Try

simple

open

floris

Use a long number instead as it has a different input.

This is a known problem (Start on boot · Issue #150 · Julow/Unexpected-Keyboard · GitHub) and when you first activate the keyboard you are told that the keyboard will not work unless the phone is unlocked first. One solution is to install one of the keyboards recommended by @Licaon_Kter and decide whether to replace it completely or to use unexpected keyboard normally and another keyboard only to unlock the phone.