Thanks for all of the suggestions (and link to other thread).
My problems began, coincidental or otherwise, a few weeks ago when I started getting regular warnings on the Mac side about insufficient resources, and the system generally would slow down and sometimes gradually freeze. (I have an M2).
Although I was running (the usual) large Windows Excel files, in the Mac warning window Firefox (Mac) and Chrome (Windows) featured highly, so I went through and closed a lot of tabs I always had kept open.
Following other advice I deleted a lot of old files, such that my hard drive now uses 760GB out of 1TB.
The warnings continued even with very few apps running so eventually I updated to Tahoe 26.4.1 and that seemed to resolve the Mac warnings problem.
Then, and this may be unrelated, about a week ago I started getting random instant reboots of Windows, like you all describe, typically several times a day and with no warning.
At first I thought Windows was trying to update without asking, so I changed that setting to ask me in future, but the random reboots continue.
I've tried as much as I can of suggestions above including increasing Parallels to 6 CPUs and 8GB RAM. I've updated Parallels (Pro) to 26.3.1 (57396).
Like others I only have one option to select or deselect "Adaptive Hypervisor" so cannot change to "Apple".
In Windows Event Viewer I see multiple lines (I don't know if that is normal) but particularly there are three 'Critical' reports all matching the times of my last three crashes - they are: kernel power event id 41.
I considered a System Restore and noted the last Windows Update was on 19 April which I think coincides with these problems starting.
I am tempted to do a system restore to roll back that update but it gives me the (probably usual) warnings that Office blah blah may not work properly afterwards.
This is very disruptive so I would welcome any suggestions please.
Thanks
