If you sort a tag by ratings, a game will appear at all and will appear higher in a weighted comparison. So 1 rating with 5 is not better than 10 ratings with 4.9. That kind of weighting.
https://itch.io/games/top-rated/tag-arena-brawler
Add to collection appears for every item at the places where this button appears. You cannot hinder people putting an item into a collection.
"related" is that recommendation thingy, no time mentinoned above. It does not appear for new games. Might take months till it appears. Criteria are unclear. But in theory it would group games together by things like tags and how people rated games with those tags. Something like that. Specifics are not known to me.