I got the first M1 MBP in May and started manual backups on a new 5 TB LaCie rugged. I have no backups before August.
Then I got the second machine, identical except 1 TB hard drive. I haven't used or needed to backup the first machine since.
Time Machine in this second machine shows no backups at all before September.
My practice over 15 years using MBP and MBA has been to perform daily manual backups into the same or similar versions of LaCie, and for a couple years, a Passport. I have ALWAYS been able to go to the data I'm looking for on a given date. Always able to copy the data to my machines.
I don't always backup daily. I do a backup when I've made a significant alteration in the data on my machine. Which might be 3, 4 or 5 days a week, or maybe not for 2 weeks if I'm on vacation.
I am floored and flummoxed that I have lost more than 3 months of my hard work!