https://itch.io/games/newest Already does this to some degree, games with major updates reappear on Newest.
If there was a section with all newest updates, it'd be filled with spam.
The post feed is sorted by newest updates. But you can't sort it further by tags.
And yes, a browse section where could do that too would be spammed. Some publishers already try to game the system to reappear on recent. They are hurting themselves, in my opinion. Deleting a game and republishing it will make you get lost on all collections, and you can't accumulate ratings. It also makes you look like a bad agent for any player noticing what you do. And as you said, they would reappear there with major updates anyways, so it is so useless and annoying.
Reappearing in “newest” is like winning the lottery. Both never happened to me. The spam can be solved by adding a way for players to block games/developers so that they no longer see them. And if the players don’t like the new section, they can continue going to https://itch.io/games/newest
You need to do a major update for that. And what is and what is not a major update is unknown to me. By observation it is not more often than once a month. And as a speculation, it might be account bound. You have many projects. So maybe most of your updates are considered minor, since you already published a whole new game that month. It might be that staff has to approve them, but I doubt that they have time for that. So maybe it really is a lottery, who knows.
This might be so. But this would also be quite unfair to the developers that simply update their games regularly without logging about it - if this were the only way to have an update be considered a major update. Even more so as devlogs have their own place to shine and be found, regardless if there is any associated refreshment of the recent status.