This game is pretty simple to install, but it does require a little bit of googling to find things and arranging files, so I've created this tutorial to make it as easy as possible :)
The main thing that you'll need is the AM2R Launcher. This can be downloaded from the
releases page of the AM2R Launcher's GitHub repository. Just find the "Assets" section of whatever the latest version is, (2.3.0 at the time of writing this) and download the file named "AM2RLauncher_x.x.x_win.zip". When it's downloaded you may unzip it.
The other thing you'll need is a copy of AM2R 1.1 (The last version released by DoctorM64) to give the launcher to be patched to the latest version. I can't directly link to this file, since it contains copyrighted assets, but a google search for "am2r 1.1 download" or something similar will provide you with plenty of places to download it. It will probably be a zip file called "am2r-another-metroid-2-remake-1-1.zip". When it's been downloaded , DO NOT unzip it, rename the zip file to AM2R_11.zip, and then move the renamed file into the AM2RLauncher_x.x.x_win folder (The folder that contains "AM2RLauncher.exe")
Now you should have a folder called "AM2RLauncher_x.x.x_win" which contains "AM2RLauncher.exe", "AM2R_11.zip", and a few other files. Once you've done that, create a new bottle within CrossOver and click the "Open C: Drive" button on the bottle's page. Navigate to the "Program Files" directory, and move your "AM2RLauncher_x.x.x_win" folder there.
Go back to the bottle in CrossOver, and click the "Run Command" button. Next, click the "Browse..." button and select "AM2RLauncher.exe" in the "C:\\Program Files\AM2RLauncher_x.x.x_win" directory. Click "Save Command as a Launcher", and you will have a launcher application in the bottle's page in Crossover!
When you open the launcher for the first time, you will briefly see a command prompt window pop up. Leave it alone and be patient after it goes away, I promise it's working. After a few seconds the actual launcher will open. Click the "Download" button to install the latest community updates. (This may take a little while depending on your internet connection) After it finishes downloading, you should see "Community Updates (Latest)" in the Current Profile dropdown, and you can hit "Play" to play the game!
Enjoy!