Imac 2012 on Catalina, no time machine

[ferrarofilms]

Made the mistake to allow update to OS 10.16 into Imac late 2012, I7, 32gb ram. Tried to go back but it was impossible, tried all I found on the web but it did not allow to reinstall from an external drive. Since I bough a mini M1, decided to stay as it was but.....it does not back up a time machine disk, again, tried anything on the web, apart from the obvious newbie things but nothing worked.
Cleaned with cleanyourmac, tried diff disks, ports, formatted, re-formatted and always the sam warn, time machine failed. First time since I moved to Mac in 2008....

 

[nambuccaheadsau]

Very confusing as there is no OS X.16, latest is OS 11 known as Big Sur. Catalina OS X.15 was the latest OS that could be installed without hacking the machine. You will be required to format external drives APFS (Apple File System) in order to use Time Machine. Have a read of this and see if there is any ghelp"=

macOS Big Sur: Using APFS on a Time Machine drive has some catches

The updated macOS finally allows you to use a drive formatted with Appleu2019s not-very-new APFS filesystem as a Time Machine destination.

www.macworld.com

 

[ferrarofilms]

My mistake, OS 10.15, I got 11.2.2 in my new M1.
Problem solved, it does not have anything to do with the formatting of the disk or the disk itself, time machine sees now two systems disk (m@c and Mac data and aborts), changing the name to the...data icon solves the problem and it backs up.
As my long life has taught me, sometimes it is better to look for yourself on the web, now much more easy than decades back, when one had to do a Chemistry library research before tacking a research.
Thanks anyway.