Hi! I don't know if someone came across this issue, but let me explain.
Earlier this year, more like in January 2020, i've come across one issue. I got an idea to play modded Minecraft 1.2.5 after many many years with my friends.
After I got it to work I found out that i have big issues with keyboard/mouse. Mouse was lagging the whole game and keyboard was freezing sometimes never even letting me press esc to get to the menu.
The only thing was that I had to do some "investigation" back then and here's the conclusion. I actually never posted anything about it, so i will now because it could help someone.
So, what versions are affected on which macOS?
I had macOS Mojave back then, i remember that it was working just fine on High Sierra back in 2018 when i tried it back then.
Affected Minecraft versions are (i think) all from alpha, pre-alpha, infdev and those to Minecraft 1.6 when Mojang sorted this issue.
I'm now on Big Sur beta, totally skipping Catalina, so i don't know now if it still works here and on Catalina, I need to try.
The first thing that i was thinking fixed the issue was older/newer Java. I installed older, newer versions and tried them only to find out that Java 1.6, the JavaApplet version that macOS had years ago was fixing mouse issues. But keyboard was still a big issue, so i had to make something.
The problem happens in way LWJGL connects to the original Java Canvas window. To fix it, i had to recompile the Minecraft.class with "removed" Java window creation and the connecting of the LWJGL one to the Java window. Java Canvas window creation is not actually removed but only disabled because if it was removed, OptiFine would crash the game. This way LWJGL now only creates it's own window and the issue is fixed with working mouse and keyboard. I don't have source code for illustration but i'll maybe try to find it.
(and you still need to edit the MouseHelper class as it is a bit connected to all of this)
And the only issue now is that you need separate recompiled .class for vanilla Minecraft 1.2.5, for Forge modded 1.2.5 and for other versions.
I don't know if i have still the Minecraft.class recompiled with the bugfix for vanilla 1.2.5 somewhere but i surely have the one for Forge for use in MagicLauncher. The Forge one is for Forge 22.214.171.124 and also has achievements fix by NargonCZ. If someone wants, i can send it or try to recompile it for other versions.
All Minecraft versions prior to version 1.6 on macOS Mojave and newer have keyboard/mouse issues that are thankfully fixable. I fixed vanilla 1.2.5 and 1.2.5 with Forge myself. The only problem is that I won't be able to fix versions that don't have MCP(for ex. Infdev, Indev), decompilable Forge or Modloader(i haven't actually looked at Modloader so i don't know how it works there) so you have to play them by using Wine, VMs, Bootcamp on real Macs, Linux/Windows on other partitions or just other machines.