You can add leading 0's to filenames with MediaMonkey itself using <Track#:2> in Auto-Organize Files.

I would test in advance: if you rename existing files, MMW may recognize them as "new", which could lead to duplicates and lost track statistics. And then you still don't have the corrected track numbers in the ID tags / in the MMW database.

I would therefore change the ID-tags as suggested, and then use "Auto-Organize" to create the file names from the tags.

Thank you for your information.
It is no problem to go over it with Powerrename. With the tens, or hundreds, I can take the files out of renaming directly in Explorer, so this little detour doesn't take too much time.
Thank you.

you will have to correct the tags manually. MP3Tag can fill track numbers with leading zeros, MMW doesn't have this option as far as I know.

when the ID tags are corrected, you can have the file names created from them.

My problem may be trivial, but I am currently at a loss.
It's about the order in which the tracks of an album are played.

An example album contains the tracks 1.mp3, 2.mp3 up to 13.mp3.
If I call the album by filename, MM plays 1.mp3, 11.mp3 and just not the correct order 1.mp3, 2.mp3 etc.
I help myself here with the Powertoys of Microsoft, in which I with a rule:

Rename (.*).mp3
to
0$1.mp3
and with three-digit numbers then just 00$1.mp3.
I just so add one or two zeros in front of each file name. It is not perfect, in the example case I have to remove the leading 0 manually for the tracks 11-13. Unfortunately my knowledge of regular expressions is not enough to get this perfect.

In general the question from me to the round: How do you do this? There must be a way for MM to play the correct album order. What am I missing here?

Thanks
Andreas