Since my previous post on the issue I've been experimenting to try & find what triggers it. I now close everything before turning off & only have finder launch at start-up. After signing in, I then make a point of not touching anything until my Macbook Pro M1 has fully launched & stabilised. Because I've stopped everything else launching then that's when finder & all the various symbols fully appear along the top of the screen (I've only done that to speed up launching/stabilisation & it's probably not needed so long as you're prepared to wait a little longer).
So long as I do that, my cursor always functions correctly. However, even momentarily touching/brushing the trackpad before that point can be enough to trigger the problem (& usually is).
Bit of a pain having to be so ultra careful at launch, but still far better than having to hold down the power button to shutdown & start again. I never had any such issue on my previous MacBook Pro (late 2013), not even once. I'd just sign in & pretty much get going straight away, but this one is currently extremely finicky.
It's not great, but at least it works, or has so far in my own case & with a 100% success rate.
One point I'd make, is that usually at launch everything displays across the top within a couple of seconds or so. Every once in a while though, it can take a few more seconds before everything on the top left appears. In my case & because I've nothing else set to launch at start that's:- the apple symbol, finder, edit, view, go, window, help.
It's on those occasions & when that extra small delay occurs that I've previously been caught out. If I touch the trackpad & everything top left isn't yet fully displayed, then it's an odds on bet that my cursor will freeze or disappear. ;-)