Here are a couple suggestions I have to improve existing UI/UX, speaking from the point of view of both a player and a designer. These are mostly quality of life changes.

I feel that the game could use a radial menu to give commands to bots in single-player.

Radial menu.
Quite often they make their own decisions that aren’t what the player needs. I’ve seen a bot ignore sentries and the crystal, which was mildly annoying, to say the least. My suggestion is to add a few simple commands, as seen on the picture. Multiplayer could also benefit from this change, if you ever decide to implement communication and ping-system for teammates.
I know that Endless Dungeon already has a similar function, but, especially on higher levels of difficulty, I found it a bit lacking, although it certainly has potential.

Pause menu.
-“Save and exit” buttons being on the top side of the menu are extremely confusing. Most videogames follow a similar structure when creating a menu, and it’s only natural that a player would expect “Exit” to be below other buttons, and “Continue” on top instead. I’ve lost my progress twice by pressing the wrong button and exiting the game. That said, a player uses the “Continue” button much more often than “Exit”, so putting it higher makes more sense to me.

- Settings always being “opened” creates a bit of unnecessary noise, in my opinion. Generally, players only use settings once per play session or less, so I fail to understand why they would need to constantly be in the spotlight. Again, that’s my personal point of view, but I don’t think someone would need to adjust their graphics or sound that often. My suggestion (as seen in the picture) would be to “hide” them behind a single “settings” button.

- Pressing “Esc” opens the character’s card first. I feel that it’s a bit counterintuitive, since usually the character menu is accessed through a specific button, like “C”, and by pressing “Esc” a player would expect to save the game, access settings, or exit. Perhaps one of the variants I’ve provided could work better.

Main menu.
- The pop-ups and icons on the right side of the main menu seem to be disconnected from the layout grid. “Friends” menu covers half of the button when it opens, and the height of it also doesn’t make much sense. “Read news” and “Friends” buttons also don’t align.
I offer a way to fix that a bit, but it’s not a finished work and simply a suggestion to improve the overall look. I drew the guide lines to demonstrate what I mean.