Use Laptop keyboard for Android device I am running Ubuntu on my notebook and Lineage OS without PlayServices on my phone.

Now I would like to use my Laptop keyboard as a remote keyboard for my phone, how could I achieve that? I guess, the phone is already ready for external bluetooth keyboards, how can I turn my Ubuntu notebook into a external keyboard?
You are looking for Bluetooth HID (Human Interface Device).

So instructions for Ubuntu can be found here:

https://askubuntu.com/questions/229287/how-do-i-make-ubuntu-appear-as-a-bluetooth-keyboard

Although its is unclear if anyone has made it work on more recent versions of Ubuntu.