Ok, so now that Mousegun is done, I've decided to make a Questions and Answers to make some things clearer to now players.
Please note that from now on, if you post a comment that asks a question that has been answered here, I will not answer ! 
So make sure you read this is full before asking for help, thank you for your understanding :

1- The game keeps drifting to a side on the Web version.

There's a known bug with Firefox that makes the camera drift on the right constantly. This only happens in Firefox.

Here's a few solutions :
- Put the game in fullscreen. This will stop the drift.
- Zoom in or out on the web page. This also fixes it for some reasons.
- Use another browser. So far I tried Opera and Chrome and it works on both.

2- Windows keeps detecting the game as a virus.

This happens when you try to launch a packed .exe on recent versions of Windows. Please use the last version of the game 1.2. This version is unpacked and shouldn't be flagged as a virus.

3- The game on Android doesn't have touchscreen controls.

This is a design decision because controlling a fast first person shooter that asks for precision would have been awful to control on touchscreen. Please connect a controller or a mouse and keyboard to your Android device to play the game. There's plenty of good bluetooth controllers out there.

4- How do I complete the game ? I can't reach 100% on my save file.

I'm sorry I haven't made this clearer, this one is on me and I'll try to make things more explicit for future projects.
-First, you need to reach the target score for each level. This target score is indicated on the Missions Menu just after the little arrow on each level. Once you've reached the target score, a message in game will appear. You don't have to find every single enemy or disk to complete a level. This will unlock the secret ending that you can access via the Extra Menu in the Missions Menu.
-Then, you will have to get a total time on all levels under 15:00. This will unlock another secret in the Extra Menu.
After all of this is done, you will have completed the game at 100%.

5- Will you ever add more levels, enemies and weapons to the game ?

No, the game is finished and I'm currently working on another game called Axyn which is a 3D platformer. You can follow my advancements on Twitter or Discord and support me via Patreon.
The only updates I'll do to Mousegun will be bug fixes.
I might someday make a sequel or another game set in this universe, but not for now.
You can always check out my previous game Clover's Space Beat which is set in the same universe.

6- The game displays a black screen on Windows.

Godot uses the Vulkan renderer. This happens if your graphics card doesn't have the corresponding driver.
If you have an NVidia card, download the last Vulkan driver here.
If not, you can search for the driver corresponding to your graphics card with a quick Google search.

Thank you for reading this Q&A, if your question doesn't appear here, I would prefer if you send me a message on my Discord as it is much quicker and simpler for me to answer you.