I just did a manual test run of my Guide Load process which runs EPG Collector and then loads the resulting file. It worked fine, collecting the data and updating MC, with the "Program guide last refreshed" time updated correctly. I am using MC21.0.54 currently.
Maybe it is a Windows 10 thing, or maybe some security software is stopping the manual run process. I have seen this before where an automatic run will work, because it isn't run interactively, but a manual run initiated by a user through the GUI would not run. Make sure your virus scanner is allowing all the MC processes to run, and set the following programs to Allow in your Firewall: JRWorker.exe, JRWeb.exe, Media Center 21.exe, and JRSerice.exe found in the "C:\Program Files (x86)\J River\Media Center 21". Also "MC21.exe" found in the two Windows directories, "C:\Windows\System32" and "C:\Windows\SysWOW64", just to be sure.
Also Steo, if you want to test the automatic run, don't set the next run time so close to the current time. There used to be (still are Yaobing?) a lot of rules around how often the Guide Load process would run, whether it would run within a certain period of a previous run, and so on. But there have been lots of changes in the load process area, so I'm not sure what the rules are now.
Since the Guide Load process can now be run as often as every two hours, I would set the next run to say two and a half hours into the future, and then leave it to see if it runs. That makes testing a long process, but that can't be avoided if the manual process isn't working for you.