As has been explained many times, that support phone number is a third party and they really suck.
Don’t waste time and/or money on them.

23 Gb free is nowadays considered not much, so that part is right although your system should work without a problem with it.

I see you are using a old(er) version of avast.
I suggest to perform a clean installation of the latest version and see if scan from the explore menu is working again.
https://forum.avast.com/index.php?topic=169255.msg1203279#msg1203279