I like this game, it has potential. I have a few suggestions, I hope they can help:
1. Moving the mouse over an object, not even clicking on it, triggers the selected action. This can lead to mistakes, like selling stuff you didn't mean to sell. This could be improved by just requiring a click for all actions.
2. The space feels way too cluttered. Objects can get under text, making them hard to see or unreachable. One way to improve this could be making a standard UI instead of fixed buttons, and tying the zoom function to the scroll wheel. That way, it feels smoother to play.
3a. This is not intuitive. It took me a few minutes to even navigate the buttons correctly, and I still had a bit of trouble up until I lost. Even by the end, I could not figure out how to upgrade my or fuse my units. I think a tutorial would help a bunch, even a small one with simple text instructions. What buttons do what, what to do with the units, all that jazz.
3b. I have no idea what half of these units do. I don't know why they turn red or green at some points. Most of them just stopped attacking and I couldn't figure out why. If it's because of the mode, and the automatic one doesn't work with guns, that's something that needs to be fixed before the player confuses themselves with a confusing option. If not, same conclusion: they need to be explained to the player.
3c. The menu system is also quite hard to understand at first. I was able to get around by the end, but it could be improved upon. Since the menu is in a tired structure, you could use tabs for the classes, show a grid of units for each class, and show a description for a unit when hovered over. That would feel a lot cleaner, and more player will be familiar with this method. If you want some more examples, my dms on discord are open.
4. Units collide with each other, making it hard to make stuff around without bumping into other units. Maybe the they wouldn't collide with other stuff when being moved, but collision goes back to normal once the player lets go.
5. As xf_p0wer mentioned, the background is a bit jarring, and could be dangerous to the wrong person. Maybe a low contrast checkerboard pattern, or some other pixel design. And if you're set on making it move, try not to make the color change so high contrast and bright.
All in all, not a bad game. Definitely some stuff to be ironed out, but I played for a good 10 minutes despite my critiques above. I like the art, the music wasn't bad, and I can tell a lot of work has gone into this so far. So, keep up the great work! I hope this has helped, even a bit.