Hi KjartanEno, totally agree it would be helpful to see back to back comparison of the M1 Mac against Intel/AMD. So, I've tried to do just that with what I have!
To be fair to many of those commenting on the M1 vs Intel MacBook debate, they are comparing the M1 against older MacBooks. I don't have such a machine to hand, but I do have a 3 year old Dell business laptop. No discrete graphics chip, just the Intel UHD630. M1 MacBook (16GB) running the LL Second Life viewer, the Dell running Firestorm under Ubuntu Linux. No fancy PyFX (got look into that...). I went to a nice forest with lots of trees/objects around, and set the graphics settings as close to each other as I could, first shadows on, then shadows off, per your challenge. Draw distance 192 for everything. Note the Dell screen resolution is smaller than the MacBook, which I haven't tried to compensate for here. Both at native resolution.
Long story short, the 2 machines are pretty similar. M1 gets 3.3/17.3 fps with shadows on/off. Dell gets 3.2/11.4 fps.
The bottom line is the M1 MacBook Pro will get you decent enough performance with low graphics settings, and will probably beat an Intel discrete graphics laptop from the last few years, but not by much (screen size may be a big factor though). If you want all the fancy graphical effects, get a machine with a discrete graphics chip. As if anyone is surprised by that!
BTW: I prefer running my gaming rig with NVIDIA RTX2060 SUPER, 4K screen etc. for Second Life, of course I do. But when I'm not at the desk then the M1 MacBook is easily good enough to log on and join in the SL fun. Way better than my 5 year old MacBook Air.
Don't let anyone convince you it will compete with a discrete graphics chip PC/laptop - it won't. However, I hope this is helpful in setting realistic expectations performance of SL on the M1.
One final note - the Dell was running the fan full bore during all of this. The M1? Whisper quiet. Nice!