[ I might make this a regular thing. No promises, though. ]
My iPad Mini 4 and iPhone SE (OG) are still on version 13.7 — I turned off Automatic Updates on both devices when I heard that 14.0 was dropping with only one day's notice. After the hiccups that version 13 went through, I'll wait a bit until the kinks have been ironed out.
My 2017 iMac is still on macOS Mojave 10.14.6, and I'm debating whether to upgrade to Catalina before Big Sur ships or continue to sit tight and wait for the latter to get a version bump or two. I've prepared a Mojave virtual machine using Parallels Desktop, which I'll use for a few Steam games. Out of curiosity, I cloned that machine last night and upgraded the clone to Catalina just to see what changed. I'll admit that Screen Time would be potentially useful to have, as I use that a lot on the iPad to control my gaming. The big question would be whether my printer would still work.
I've removed one possible pain point that was holding me back from Catalina — I recently switched from Apple Mail to Mozilla Thunderbird, and the latest version is working well for me. Those who were put off by the old-school looks of Thunderbird probably won't be turned by the new version, but I'll take functional over pretty any day.
The integration between Apple Mail and DEVONthink was nice to have, but I can do that just as quickly by saving emails to DEVONthink's inbox folder.
I've been experimenting again with Linux, with a view to keeping this iMac working once Apple stops supporting it. I've got an external SSD I can use, so I don't interfere with macOS. Dual-booting is a pain, though, and I've held off from installing rEFInd because it requires temporarily disabling System Integrity Protection (SIP), and I'm not sure how well that'll work once I upgrade past Mojave.
Linux Mint works pretty well, although the built-in sound doesn't seem to work. Luckily, the output monitor on my Blue Yeti microphone does work, as does my Bluetooth headphones, although I'll stick to the former to avoid re-pairing every time. I could even play some modern Steam games, which pleases me a lot!
My mum's Android phone stopped playing notification sounds the other day after a system update. I spend ages checking various settings and sending messages from my iPhone via WhatsApp to test, but nothing seemed to make any difference. In the end, I restarted the damn thing and sound notifications worked again. Go figure.
I am very glad that I no longer do technical support professionally, as stuff like this would drive me bonkers!