Very nice Blick - congratulations.
The presents still under our Christmas tree are too small to contain a new iMac
so to at least give it a new feeling, I decided to upgrade the 'old' one (27", late 2012) to Catalina instead.
Since it did collect quite a bit of rubbish over the years (I bought it with Snow Leopard) I decided to do a true fresh install:
- copy the 'Documents' and one or two other folders (e.g. Music, Web site) with personal files to an external disk (I keep all my photos on an external disk already)
- make a list of all Apps I want to keep (and check for 32-bit ones)
- ensure the TM and Cloud backup are up to date, then disconnect them.
- format the main (1.12 TB Fusion) drive
- Install Catalina
- Download and re-install all Apps
- Copy 'Documents' + other folders back onto the main disk
- Check if all works (for a day or 2)
- Reconnect the TM, and re-enable Cloud backup
All is working fine since. My iMac seems faster than before and I've freed up a few hundred GB of disk space.
Jos
P.S. WC was out of scope here, as it is running on a 'headless' Mac Mini.