OS Catalina update 'lost' my Lightroom catalogue file

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Yesterday I connected top the iMac for the first time since mid December and went to do some editing. When I opened Lightroom it couldn't find my Lightroom Catalogue file. So I went and looked for it manually on the SSD I swear I'd put it on and I found nothing. I went to my backup drives and the latest Lightroom Catalogue file was dated May 2020 with hardly any of 2020's RAWs in it. Having looked in finder it bringing up Lightroom catalogue files but no recent files. I admitted defeat and yesterday evening I started to rebuild from the May 2020 catalogue file knowing I've haven't edited that many images this year anyway so it wasn't the worse that could happen.

This evening I thought have another go with finder and I found a Lightroom catalogue files dated December 2020. It was in a relocated security folder on the SSD. The folder contained this document:

Screenshot 2021-01-02 at 17.15.28.png

It seems during the OS update to Catalina I did in mid December it relocated my Lightroom catalogue folder to another place on the same SSD. I'm not sure why it do this. As I'd not used Lightroom since I'd not noticed the catalogue file had been moved.

Through my own fault my last backups were dated May 2020. I'd rearranged my desk in march to enable me to work from home. As I've not been using the iMac I'd put it away in the corner to create space on the desk for the works laptop and another screen. Since then I'd only bought out the iMac occasional to add new photos when I'd used the camera which wasn't very often in 2020, never reconnected the backup drives. Well lesson learnt, backups must be done as its not just hard drive failure that can cause failures/lost of files!

Its also pushed me to finally get a replacement for my failing Lightroom drive. Previously I'd partitioned it so there was a RAW section and a catalogue section. The catalogue partition section failed at the beginning of 2020 bring up an error message. I've been procrastinating whether to replace the Mac with a PC or get another drive. I've now ordered another drive as I've decided a Mac mini would be a good replacement that lets me keep a single monitor for both the works laptop and Mac for photography.

This is the first proper issue I've had with a Mac in 8 years which isn't bad. Any ideas why the OS update relocated the Lightroom catalogue folder?