How to set up file sharing on Catalina 10.15.7

The three methods of connecting to a shared computer are:

• Connect as a Guest
• Registered User
• Using an Apple ID

They appear as options when you press the "Connect as..." button.

They are described on this help page: 

• Connect your Mac to shared computers and servers - Apple Support (CA)

Thanks for trying. Not sure its a network issue since screensharing, Media sharing and airdrop are working fine. It's only file sharing that cannot be enabled in preferences. The clipboard is also being shared between these computers. Regardless of whether there is a problem with my setup, there is a bug or design error in the preferences GUI for not raising an error or showing a message when the checking of a box is not possible. Ideally, from a GUI design point of view, a checkbox should be greyed-out if it is not checkable. If not, the checkmark should appear when you click it!

I do not have any firewall software. Also the VPN I use for university is disconnected.

As explained in the question, the main problem is that I cannot enable file sharing on the MacBook Pro from which I want to copy a file. The video linked in the question shows what happens when I try to select 'file sharing using AFP'. Here are some screenshots in case you can't see the video:

1. in the file sharing options dialog

1. After pressing 'done'

It is impossible to turn the File Sharing checkbox on within a few milliseconds of checking it, it is unchecked (see video).

Also, I should mention that initially, when I first tried to view the files on the MacBook Pro from the Mac Mini, file sharing was already turned on on the MacBook Pro. However, no folders were selected so I added the Downloads folder (which is where the file is the I want to transfer). Still it did not work even though the File Sharing checkbox, at that time, was checked.

Then I went into the options and tried changing from 'Share files and folders using AFP' to 'Share files and folders using SMB'. At this point it unchecked both and File Sharing became unchecked. Neither can be turned on now.

Thanks. I tried that. Screen sharing can be turned on and off (and also works fine, I tested it). Only File Sharing and now Media Sharing can't be turned back on after being turned off. Must be a bug somewhere. You expect a GUI to raise a warning or message if a check box can't be checked. Not do nothing.

I also tried restarting and that didn't help.

I gave up in the end and waited for the 15 minute AirDrop to complete (making sure neither computer went to sleep during the transfer!).