Instability issues since upgrading to Monterey.

Hi All, since upgrading to Monterey I have had so many issues I just don't know where to start.

Up until this upgrade, my iMac (Retina 5K, 27-inch, 2017) mac ran like a dream. Because of issues, I have tried a fresh install with no luck. The OS runs on an external SSD on one of the thunderbolt ports which it has happily done so for 4 years.

When I originally installed it took several attempts as it would just hang for hours then reboot and start its install again, it was only when I did a fresh install rather than an update it seemed to get somewhere.

So starting from boot, the Mac seems to stall halfway at the progress bar will not move for about 5-10 minutes then eventually boots. Once booted it does seem a gamble how long it takes before I hit any issues but the most common one to start will be the blue tooth mouse and keyboard becoming unresponsive with the spinning beachball making its appearance then eventually telling me the mouse and keyboard have disconnected followed by a few seconds then reconnecting.

Looking in the console I have repeated bluetoothd - reports, I have attached one. Once the keyboard and Mouse re-connect the machine will be usable but I now and again the spinning ball will return. The machine its self just feels unstable, with periods of 'input lag' and spinning balls and on occasions I just have to hard restart as it just freezes.

My apologies if have not included the correct logs, I use to be a windows guy and made the switch to Macs about 10 years ago and I have never had issues where I have had to look into logs or anything, at present I'm feeling like I'm back on an old windows machine.

Like I said I don't know where to start really. I'm hoping there will be something glaringly obvious to someone who is more used to troubleshooting macs.

Just to re-affirm. The Machine had been working with zero issues until I upgraded, when I had install issues I hoped a fresh install would help; it did not. there has been no hardware configuration has changed and I have tried the various re-set procedures.

I would be grateful if anyone could help me navigate these issues. looking at the log is there a possibility that the machine still thinks its upgrading and its stuck in a loop?

Many thanks

Lee