This pm I took a huge gamble. I installed PostmarketOS, a mobile linux distribution, on my OnePlus6. It's buggy but I wanted to have a play around. Very easy to install via their web flasher.
Unfortunately, it's very buggy. Not many usable apps yet for my purposes. After playing around though & investigating I realised that I could install Waydroid. Game changer as Waydroid installs a LineageOS container within PostmarketOS. That way I had access to all my normal apps via F-Droid. Result!