I have a bunch of challenges to keep track of all the different series I am reading, I would loveee to be able to sort them into a group / tag them to filter easily when looking through all my challenges

I would love to be able to sort challenges! I just created one that's more of a long term thing for myself, but now it's at the top of the list, pushing down the ones I'm actively working on.

Would love more of a manual sort like the Up Next.

I would also like to be able to sort reading challenges by close date, so that I know which ones I need to prioritize if I'm going to finish them!

Yes please! I've joined a bunch of challenges but I'd love the option to reorganize them such that my most frequently visited ones don't appear under "show more" several times. Where some of my challenges I'm actively working on, and others I have to keep track of lists more passively. I can leave and re-join the ones I want on top, but that's not an ideal workaround.

Would also also love this! I'd really like to filter challenges by dates ending like @emfass said below too would make it much easier to keep track of!

Would also love this. I'm diving into challenges more for personal long-term goals (reading through an author's backlist, reading the books I own, etc.), but now I've excitedly joined a lot of challenges and it's hard to muddle through the add-to-challenge menu in the bottom left. Changing it to alphabetical order by title, or ones with soonest end dates on top, etc. would be really really helpful! I'm finding the listing by most recently joined at the top is not helpful to me at all. :)

Additionally sorting within the challenge itself for complete / incomplete prompts would help too! Some have a lot of prompts and it can be hard to quickly identify which ones you have left