And this time untick the ~100 or so games I do not plan on playing through.
Rather than having to click "Add to completion" and fill in time it took me to beat them.. thats tedious and takes waaay too long!

I can clear all of the games out of your collection, if you want. I'm about to step away from my computer for the night, but I could do it tomorrow morning, just let me know.

If you're just looking to mark things as completed, you can use the Quick Edit feature to toggle the progress status, rather than having to enter a completion time. That would, of course, still require time to do, but perhaps a bit faster :P

I'll check out the Quick Edit, if I find it.

Would it be possible to add the option to Tick multiple games for completion?

And it would gather the Time Played from Steam on those games?

Or just as Completed.
I just removed ~350 games from my Backlog, and just doing that was tedious!

Would be nice so you dont have to manually do each, one by one and have the entire page reload everytime.

I like the idea of a bulk edit, but I've been trying to set up the Collection Search page so it's very efficient at making quick edits for the most commonly changed properties. Backlog is one of those properties and it can be toggled with the button on the far right-side of the screen. Toggling this button should not require the page to reload each time. Likewise, the Quick Edit feature (button on the left) should not require the page to reload.

I'm intrigued by the idea of pulling in time played from Steam. Currently, there isn't a place to store just "total playtime". We could take that data in, but you'd have to create a completion off of it. So maybe some sort of wizard that let's you pick the games you want to pull playtime from Steam for and then you have to fill out the completion info for each one (which is basically just an optional completion date and the completion type).