The M1 will be my home computer as well as a portable device.Would you know if its safe enough ti leave it plugged to the mains most of the time.?
Safe...yes. A good idea? Probably not.
Apple recommends not leaving their laptops plugged in all the time as this will decrease the life of their lithium batteries.
And that is consistent with the general recommendation for just about all lithium ion batteries in just about every application. It's best to avoid charging lithium ion batteries over 80% or letting them discharge under 30%.
They also do better if the battery actually gets used, rather than using power from the wall socket. (This is often described as "Lithium ion batteries live longest if you keep the electrons moving.")
From Apple:
http://web.archive.org/web/20130425025000/http://www.apple.com/batteries/notebooks.html
"For proper maintenance of a lithium-based battery, it’s important to keep the electrons in it moving occasionally. Apple does not recommend leaving your portable plugged in all the time."
"Long-Term Storage
If you don’t plan on using your notebook for more than six months, Apple recommends that you store the battery with a 50% charge."
https://lifehacker.com/5875162/how-often-should-i-charge-my-gadgets-battery-to-prolong-its-lifespan
"...lithium-ion batteries do best when you discharge them for a little bit, then charge them for a little bit."
"Similarly, lithium-ion batteries don't need to be charged all the way to 100%. In fact, they'd prefer not to be—so the 40%-80% rule... is a good guideline. When possible, keep it in that range to prolong its life as long as you can. And, if you do charge it to 100%, don't leave it plugged in."
https://www.popsci.com/charge-batteries-right
"Shallow discharges and recharges are better than full ones, because they put less stress on the battery, so it lasts longer. When your battery is discharging, Battery University recommends that you only let it reach 50 percent before topping it up again. While you're charging it back up, you should also avoid pushing a lithium-ion battery all the way to 100 percent."