Kay'.
You say it's easy, but do you have a proof of concept and/or code?

Sorry I don't have a development team, and I personally don't know how to do something like that. Sounds super complex and you probably need to master one or more esoteric programming languages and tools. Yikes!

Besides, what's in it for me? To me that sounds like a lot of work, taking maybe weeks if not decades. I could be dead before I am able to finish it you know, and I want to spend the last days of my life with my loved ones, not coding some stuff that I just can't get to work.

It's a good idea.

Say I ordered my library and then refunded a game, and bought a different game. What order_number (as you call it) would the new game have?

Good luck with that request: https://www.gog.com/wishlist/site/keep_or_bring_back_manual_sorting

However, this userscript supports manual sorting: https://www.gog.com/forum/general/adalia_fundamentals_fixing_gog_so_you_dont_have_to/page1

Drag and drop can work fine if your library is small, but once it starts growing, it becomes kind of pointless. It’s just not practical to manually move things around when you’re dealing with multiple pages of games.

I think the functionality you're looking for can mostly be handled with tags. You can mark games as favorites and then filter to show only those. And if you still feel the need to sort within your favorites… well, maybe you’ve got too many and might be worth adding some extra tags to break them down into smaller subgroups.

By the way, this drag and drop feature actually existed on GOG in the early years, but it was eventually removed.

Also see previous threads
https://www.gog.com/forum/general/bring_back_the_manual_setup_option_in_the_game_library_please is still being bumped occasionally, was even earlier this year
https://www.gog.com/forum/general/manual_sorting_in_games_library and https://www.gog.com/forum/general/bring_back_manual_sorting fell to inactivity
And yeah, would be a great thing to bring that back. I'd want to still be able to sort titles tagged as backlog in a rough order of preference, titles from the same series together, definitely would want to have completed titles sorted in chronological order of completion...

Just to show how implementing this can be trickier than it looks, let’s imagine a situation where you have multiple tags, and each one can have its own specific order. Take The Witcher series as an example:

- "Favorite" tag group: TW3, TW2, TW. The order shows how much each game is liked, from most to least favorite.
- "Completed" tag group: TW2, TW, TW3. The order reflects the completion date, the first was played earlier, the last more recently.

This works fine when you're filtering by a single tag.
But what should the order be when no tag is selected?
What if both tags are selected?
And what if you select those two plus a third tag, adding another order to the mix?

The issue is that each tag can have a different and conflicting order. So to make this work, each tag would need to save its own sorting logic, and even worse, each combination of tags would ideally need its own defined order too.

"Sort by" is a single item selection. Select manual and you just have the manual sort, no other.
Not that it couldn't work even with multiple sorting options. The manual sorting would be a single value, and if you filter or choose a different primary sorting option, with manual being secondary, that'd still apply. If you have games 1, 2, 4 in tag A, 3, 5, 7, 9 in tag B, 6, 8, 10 in tag C, if you sort by manual order, they're 1, 2, 3, 4, 5, 6, 7, 8, 9, 10; if you sort by tag order they're 1, 2, 4, 3, 5, 7, 9, 6, 8, 10. And tag order already takes the top tag into account, not all that apply to a title.

I guess it is a bit of a Steam mentality thing, sorting your online library.
Me, I download all my GOG games, so that I get the true DRM-Free benefit, and once downloaded, they can be entered into one of many databases out there, where you can sort in various ways to your heart's content.

In any case, GOG seemingly don't have the resources to do many things they should, so as always, better to do it yourself.

Tags is the way to go with your GOG online library or search via names or tags or both.

What does that have to do with steam? Has to do with wanting to be organized, and maybe something with a collector mentality if you will, wanting to have a display even if they're digital goods.

Having options is always a good thing - but...
... if together with this kind of UI/UX tinkering we also have a performance impact, please, don't.

I'm personally quite tired of bloated sites designed to hold 5 sec attention span people attention.
It gets annoying when simple sites should exhibit direct links but instead opt for a more graphical approach and behind the scenes we have so many calculations through JS that it consumes CPU and GPU for nothing really.

Have you seen the new Nexus design?
Candy for eyes, sure. But its bloated and heavier because of the code it uses apparently

Steam is also famous for having bloated store/forum pages.
Specially after they added the community 'features'.