Domoticz

I still run Buster, not sure if I can simply upgrade on that.

If you are on Buster it definitely is time to update your system......
You can buy another SD card and install everything new. then you have your old sd card as a backup.
I have no idea how complex you have made your domoticz environment with all kind of scripts and plugins but by copying your old domoticz.db file into the new and up to date domoticz system you get everything working again. You probably have to install your python plugins with required python modules before you do that.

OK, I guess I'll have to bite the bullet an do that.
The good news is the fact that I have a spare PI-4 with SSD ready for this... so I can do the install in parallel to the production hardware, and switch SSD for testing! I do have a spare RFLink, but only own one Conbee stick...
Still will take some work. Domoticz, Node-Red, OpenVPN, Monit. Installing and testing will keep me off the streets for a day or so!