MC 21 is started from the autostart folder.
I hope you mean MC is started via the MC "Options > Startup > Windows Startup" settings, rather than putting a link in the "C:\Users\[UserID]\AppData\Roaming\Microsoft\Windows\Start Menu\Programs\Startup" directory. Because you should use the MC settings for that.
Is this fixed in newer versions ?
There were a lot of changes and fixes for high DPI and high-resolution displays throughout MC20 and MC21, then a few more in MC22 and MC23. Have a search through the
Release Note Summaries and you will find them. Just search for DPI in the summaries. Use Chrome and it will show you how many matches there are down the right side in the slider bar.
Basically it looks like most of the fixes were done by the last version of MC21, so ensuring you have that as Jim says would be a good idea.
An upgrade and conversion to the 64bit version wouldn't hurt though!
(As long as you aren't dependent on any third party 32bit plugins.)