I did see WinSCP performs the correct MDTM command, so I now suspect the FTP server.
This call can be closed.

So how does WinSCP behavior differ to that of Total Commander?

The difference to ftp is obvious. If you want to reproduce that in WinSCP, just turn off Preserve time transfer settings:
https://winscp.net/eng/docs/ui_transfer_custom#common

Please see the attachment.
I see it does a correct MDTM 20220405191120 Lorem-ipsum.txt
I also see the FTP server does not reveal a time of day, but the year number.
So WinSCP might be working properly.

(Note that it does not matter when you created/touched the file, as Windows ftp client does not preserve the file timestamp, when transferring).

Yes, I know, of course it does not.

Please post WinSCP session log file.

(Note that it does not matter when you created/touched the file, as Windows ftp client does not preserve the file timestamp, when transferring).

It seems WinSCP does not correctly handle Daylight Savimg Time when uploading.
Since my country (NL) switched to DST, it seems a file's date is incorrectly set when uploading.
I created/touched a file at 12:37 local DST = UTC+0200.
I uploaded it using the Windows ftp client, which shows a time of 10:37.
That is the correct file time in UTC.
Total Commander correctly shows the very same UTC timestamp: 10:37.
WinSCP shows: 11:37, which is UTC+0100, i.e. neither UTC nor my local time UTC+0200.
My home page is a PHP script that determines a file's age.
When I upload the file using built-in ftp or TotCmd, it shows the correct age.
WinSCP transfers the local file time to the server, which ftp and TotCmd do not.
But when I touch the file and immediately upload with WinSCP, the file is shown with a negative age.