I like the game overall, but I think I found some things that can be improved.
The enemies can spawn right next to you and hurt you without being able to react. I would have a spawn radius around the player where enemies are not spawned or moved away from the player.
The enemies can spawn outside of the playing area and are stuck outside. I recommend having it either by a one-way wall or limiting enemy spawns to the arena.
In the blackout mode, the border to the arena is not shown. I got confused about why I stopped moving as there was no indication of a wall.
You can still take damage even when you have the shield. This can cause your death if you are at one health.
I recommend deactivating the player's hitbox and reactive it at the end or something else.
Having to move the player to use the start menu feels weird when all other menus use the mouse, and it is slow and not intuitive. I was confused about why, when I clicked start, nothing happened, and maybe even though the game was broken. It might be better to just use the mouse or do both, but I don't recommend doing both.
I wish you luck on whatever you do next. Have a nice day.