So, I tried the Regolith DE (mostly to see if I could get on with i3, spoiler: I still can't).
I installed the DE following the instructions here via Option 2.
When deciding it (still) wasn't for me I followed Uninstallation instructions further down the same page.
All is well. However now when opening my laptop I put my password in to login via the usual Mate greeter/screen. It will then go to desktop for about a second before sending up a second login prompt, this time via the greeter/screen that Regolith used. Has the uninstallation missed some config file somewhere? Is there an easy fix for this?
I realise this may be best suited posting on Regolith's support channels but thought I'd try here first.
I don't mind putting in a password twice but it is growing a little thin already.