Summary - the web extension never turns blue or black after upgrading the server from 9117 to 9300.
Looks like I busted something with the upgrade from build 9117 to 9300. Passwordstate itself is working as expected - it's all still branded / coloured correctly, and it does show up as build 9300.
The settings under Adminstration show that the browser extension is enabled for all:
But the extension (I'm using version 9117 from the Microsoft Edge store - https://microsoftedge.microsoft.com/addons/detail/pbbamlchainnpdodbeobfpgcpffpclka, on Edge 93.0.961.10 (Official build) dev (64-bit) in case it's relevant) stubbornly refuses to change from red to black even after a reinstall and clicking on the "Confirm" option for the URL. The server error console is empty.
Any suggestions?