This is a walkthrough on how to get various modding tools to work on Linux by using Steam and Proton.
I'm assuming you have a cursory knowledge of filesystems and unzipping files.
These are not the only methods that work! There are a few ways to get this running, but these are the ways that worked for me.
All the way at the top, click Game --> Add a Non-Steam Game to my Library --> Browse
Navigate to wherever you unzipped HD2MM and select the .exe
Setup Proton for HD2MM
In your Steam Library, right click HD2MM
Click Properties (This is where you can give it a cute name :3)
In the menu on the left, click Compatibility
Click Force the use of a specific Steam Play compatibility tool
Select a Proton version (I use GE-Proton because that's what I use for the game itself)
Launch HD2MM through Steam
At this point, the HD2MM window should appear and work as it does on Windows. The only difference is the file pathing.
From this point on, follow the regular guides on how to use HD2MM.
When running Blender natively, trying to add the SDK will throw a missing HDTool_Helper error.
All releases of Blender can be found here, but you don't need that for this method.
Install Blender through Steam
By default, this will install v4.4, which is not compatible with the SDK. Rollback to v4.0 by:
In your Steam Library, right click Blender
Click Properties
In the menu on the left, click Betas
In Beta Participation, open the dropdown and select "v4.0 - Stable"
Setup Proton for Blender
In your Steam Library, right click Blender
Click Properties
In the menu on the left, click Compatibility
Click Force the use of a specific Steam Play compatibility tool
Select a Proton version (I use Proton 9.0-4 for no reason)