External monitor causes slowdown after upgrade to Monterey
I use my Macbook Pro (16-inch 2019) connected using a USB-c to DisplayPort cable to a ASUS PB287 28" monitor which I use as my primary monitor (i.e. with the MBP shut) at the office.
Since upgrading to Monterey from OSX 11 I have found that every 4th or 5th time I power up my Mac it starts up correctly then becomes extremely slow and unresponsive.
There are no processes using CPU time or memory - it takes about 5 minutes to start Activity Monitor - and the only solution seems to be to shut down Monterey, often by opening up the Mac and pressing the power button for 5 seconds as the "Shut down" menu, once it actually appears, takes forever to even think about shutting down the system.
Once shut down the next boot is, most of the time, normal and I can get on with work.
This has never happened while using the Mac open as a laptop so I'm assuming that it has something to do with the external monitor, although what I have no idea as this monitor worked perfectly using Catalina and Big Sur and only became problematical after upgrading to Monterey.
Anyone have any bright ideas that don't include buying a new monitor to try?
Thanks