Mac keeps shutting down randomly

Hello everyone.

Today I come with a rather weird question, this has never happened to me before in all of my years using Mac computers. I have a Late 2013 MacBook Pro with a 2.6 GHz Quad-core Intel i7 with 16 gigs of DDR3 RAM, as well as an NVIDIA GeForce GT 750M 2GB. I have the latest MacOS Big Sur update installed (version 11.7.8) as well. Ever since one or two days ago, during the middle of me using it, my MacBook has shut down multiple times out of the blue, saving none of my work. Upon restarting it I don’t have a “your mac restarted because of a problem” notification either. It led me to believe I had obtained a virus but I have not downloaded anything on the computer within a month or two. It didn’t overheat, I have an app that lets me keep track of the temperature (which is medium most of the time) and allows me to control the fans. Anyway, last night I got kind of tired of it and I re-installed MacOS onto my computer. It didn’t help. I opened it up this morning to edit a video in iMovie, and so far it went well until it happened again. It isn’t the ‘Put hard disks to sleep when possible’ option either, and my mac has a good 70 gigs of space left. It has a 500GB SSD. If it is useful to know, my battery life is very significantly reduced and has been for well over a year. I rarely use it without the charger plugged in, though. One problem I used to have was it randomly turning on and opening apps, playing music, playing games and that sort of stuff but that has only happened once in the past 3 months. It would happen every night. But not anymore.

Can anyone come up with an idea of what is happening and how to fix it please?

Thanks,

Sadra

(P.S: This Mac has been used since it was bought when it came out, I had it given to me 3 years ago when it wasn’t being used much anymore)