canonical link is confusing

the smartcrawl says that my canonical is redundant (see here: https://www.webtennis24.com/wp-admin/admin.php?page=wds_checkup#tab_checkup). in my theme options (divi) it is not enabled; should i enable it?
no matter how much i read about it, i don't understand what i'm supposed to do with it. can you please clarify for me whatever i should do with this subject?
i want to add that all my broken links (404) are being re-directed (most of them) to the front page of my website (webtennis24.com). i'm not sure whether i'm doing it right, therefore your help would be very much appreciated.
thank you!
p.s. support access is enabled. so please take a look. thanks again!