Nine weeks ago I replaced Emily's 9yo 11" Air with a 2021 M1 Air. Shortly after we passed the return date I realized I'd made a bad decision. The M1 Air panicked so often that it's forever known to us as "Crashy" the M1 Air. On some days Emily would see a spontaneous restart several times a day.
I don't think it's a hardware problem; among other things it's passed repeated hardware tests. I suspect using Migration Assistant to move from High Sierra didn't help, but I don't think that's all of it. There's something bizarre with residual parental controls on my son's account that I can't seem to clear -- but Apple's parental controls/Screen Time have been horked for my family for years across iOS and now macOS. I don't think that's all of it.
I think it's mostly a bug with Fast User Switching and maybe Chrome/Google Software. We know that Fast User Switching can kill Mail.app spotlight search until corespotlightd is restarted, so we know some defect is leaking across user sessions. We also know that Fast User Switching is disabled by default on Big Sur, which suggests Apple is worried about it. (Maybe the weird Screen Time behavior is playing a role.)
So after doing every possible fix short of wiping the drive and reinstalling data from backup I removed every trace of Chrome and Google software  and I turned off FUS. Since then we've had no more crashes.
Eventually I'm going to restore FUS. This is a multi-user machine and we want it to work properly. When I do that I'll make every user admin because Big Sur does not display a Panic report to non-admin users -- then look for a log report. If Crashy stays up then the finger points to Chrome.
I really wish we'd bought an Intel Air. The 2020 Intel Air was basically perfect.
 My son used Chrome, Emily is Safari only. After one crash Emily was asked if she wanted to restart Chrome -- but she wasn't using Chrome. Suspicious for more leakage across user sessions.
Update 4/19/2021: Removing Chrome and disabling Fast User Switching eliminated the panics. We are doing ok without both so we aren't doing further testing. I don't miss Chrome and Emily and my son don't mind logging out.
Update 6/18/2021: By Big Sur 11.4 Crashy was fixed. We're keeping the name however. Fast User Switching is on but I never did reinstall Chrome. We bought our M1 Air around Jan 20, 2021 and 11.4 came out 5/24/2021, so it took five months for Apple to fix the damned thing. Eclectic Company wrote an article about M1 instability under Big Sur.