The license is problematic

[Hedwig7s]

Simply put, the license is vague and potentially unenforceable
Specifically:
1:

The Software may not be used to get a) a commercial advantage, or b) monetary
compensation.

What is "a commercial advantage" or "monetary compensation" defined as? Can I call or modify the mod from another mod with commercial features? Could a paid or freemium client offer the mod as a download able? If I'm paid to make a modification of this mod that's redistributed free is that allowed? Can I host this on my own github page if I have a donations link on my main page?

2: This license seems to be derived from snippets of MIT, but all mentions of sublicensing and redistributing have been removed. So, I can modify it, but can I then redistribute it? Can I make a fork? Am I allowed to make a competing mod based on this code? Am I allowed to make a fork to fix a bug or contribute back? Am I allowed to make modifications but only for myself?

I'd recommend expanding on these 2 topics (maybe see how other licenses handle this) to be a lot more explicit in what is and is not allowed

Better yet, use a standard battle tested license like CC BY-NC-SA

[tr7zw]

To the 1 part: this is/was to prevent certain monetized clients to use GitHub releases or so in their automatic installs. Modrinth api etc is not affected by this. Same reason you can publish mods to Modrinth/Curseforge as All Rights Reserved, and anyone is allowed to download and use these mods. Probably not needed for anything and could be removed later on.
To the second part: yes, its basically MIT but no sub-licensing or redistributing. So no publishing forks to Modrinth or CF/redistributing binaries of the mod etc. Just see it as ARR (All Rights Reserved) in that regard. The same applies to "Am I allowed to make a competing mod based on this code?". No, same as ARR. "Am I allowed to make a fork to fix a bug or contribute back? Am I allowed to make modifications but only for myself?" that yes, you can modify the code, compile it and use that binary (and ofc make a PR).

Goal is/was to not allow redistribution (like ARR), but give some freedom with messing with the code. That's why any open source license/CC license won't work, since they all by definition allow redistribution. If you know a more battle tested license that does that, let me know, back in 2022 I wasn't able to find anything.

[tr7zw]

(Obligatory, I am not a lawyer, that's why went with MIT - what I don't want, since not granted in the license = not allowed)

[Hedwig7s]

(Obligatory, I am not a lawyer, that's why went with MIT - what I don't want, since not granted in the license = not allowed)

This is still problematic since licenses are up to interpretation + can be affected by how it is enforced

Since you don't explicitly block redistribution and people can fork the project on github for personal use or PRs it's then ambiguous what is and is not permitted
For this I'd recommend explicitly allowing copying, modifying, and/or use the code for personal use and contributing or submitting modifications to the original project and explicitly disallowing the redistribution of code or pre-built assets outside of contribution
This basically covers non commercial but you could also include that you are strictly prohibited from deriving any financial gain from the project (likely want to derive that from an existing NC license)
Also you should christen it with a version number if you update it

As for licenses that would likely do what you want there are the BSL, FSL and PolyForm (probably Shield) licenses

[tr7zw]

Since you don't explicitly block redistribution and people can fork the project on github for personal use or PRs it's then ambiguous what is and is not permitted

I mean, you can always fork any Github project/open a PR to any repo. I don't think a repos license could say that you are not allowed to, since you as the uploader of the project give to Github the license to publicly display the source code, and allow the basic Github functionality.

I'll take a look at the other licenses once I got time, I did see PolyForm used by Sodium, but that didn't look fully right for what I want. Otherwise, might just simplify the license down for less confusion to really just MIT without the keywords, aka:

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software (in source or binary form) and associated documentation files
(the "Software"), to use, modify and compile the Software, subject to the
following conditions:
The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.

Other option is to just remove all confusion and change it to ARR like for example https://github.com/henkelmax/simple-voice-chat .

[Hedwig7s]

Other option is to just remove all confusion and change it to ARR like for example https://github.com/henkelmax/simple-voice-chat .

That would likely be more problematic given the current license is at least a bit more specific in do's and don'ts
E.g. if a project forks off and becomes notable and you don't negotiate a license or take it down if later on they do an action you don't approve of (e.g. adding donations to themselves) then they can argue you took to long to action it and it wasn't clear that you intended to block that use case

[tr7zw]

I don't think it's more problematic, probably it's a lot clearer in intent and thereby less confusing.
Also, you don't suddenly get fair use or something because something wasn't clear/there was no action.