I tried doing a dual boot to Mint awhile back, I did the mint backup at the start like it suggests, changed some things, broke it, restored from the backup thinking it was great id already made one, and broke the WHOLE pc.
I had to pull the battery on the BIOS to get it to go beyond a black screen when turning on.
It was terrible.
It seem to recall at the time recommendations about not doing dual boot, and if you wanted to dual boot, remove the main OS drive when you install Linux. Then put it back in.
Kinda defeats the purpose of doing it private and local.
I wouldn’t trust any claims a 3rd party service makes with regards to being private.