Yes, I already knew this, but we are very different DMs! Some of what you think 5e lacks I see as some of its best assets! Also, I only play in person and that makes a difference.
1. Encounter building rules that work
I love the fact that in 5e I don't have to work about encounter building rules at all. I design my adventures, campaigns, and worlds just like I did 30+ years ago in 1e/BECMI. Just do what makes sense for the world. And it works so much better with 5e than it did back then! This is one of things that is keeping my away from PF2e - I don't want tight encounter building rules!
From corresponding in another thread I have come to realize that we play 5e like an OSR game. I'm guessing that is not your jam and that is OK, but it works for us.
I never play with magic items that can be readily bought and sold, so this not I need for me. I guess 5e lacks it, IDK. Magic items are always quest items of some sort in my games (but we play a low magic setting too).
3. Options for robust tactical combat
We are generally more interested in strategic combat, but this his hard for me to judge. I would say 5e has enough tactical choices for us, but we hail from the 1e days when there were none and we have some house-rules that add some. That being said I think the RAW battlemaster has plenty of tactical options and the 2024 rouge is looking shocking tactical (and 2024 fighter adds quite a bit as well). We haven't decided if we will add the 2024 tactical updates yet though.
4. Exciting and unique monsters
5e RAW has plenty of that IME (no to mention all the 3PP). However, my own designs are better than I have seen from any bestiary (in any system) and its one of my favorite things I do in my DM downtime. So, I'm all good here.
5. A challenge dial to make the game, well, challenging
I know you struggle with this, but I don't have an issue here by RAW or with our house rules. I find it very simple to adjust a challenge in 5e.
Not trying to change your mind, I know your burnt out on 5e. Hope you find something that works for you better!