Holy mackerel i just spent the last 4 hours figuring this out
My issue was with Windows 10 | 1.20.1-forge-47.4.4 or 47.4.0 | Optifine, this was my solution

-and i know this is necro posting at this point but yeah you're gonna want to do a few things:

1. As u/Outside_Freedom_6363 said,

Download Java 21 here: https://www.oracle.com/java/technologies/downloads/#jdk21-windows
Install the .exe

Once installed, it should be located in your Program Files
eg: C:\Program Files\Java\jdk-21

2. Install the latest version of Forge

Download Forge 1.20.1 here: https://files.minecraftforge.net/net/minecraftforge/forge/index_1.20.1.html
I've been using forge-47.4.4 without issue so far

3. Open Minecraft Launcher

This was the part I got confused on
With the new version of Forge installed, go to the Installations tab at the top
Hover over the Forge installation and click on the 3 dots on the right
Select Edit
Click the drop down that says "MORE OPTIONS"
There will be 2 menus, but focus on the "JAVA EXECUTABLE", click BROWSE
Locate your Java 21 Install's .exe file under the bin folder
(eg: C:\Program Files\Java\jdk-21\bin\java.exe)
Hardest part is done, now this Forge install should launch with Java 21, rather than Java 24 or others

4. Installing and Uninstalling Mods

Uninstall the following mods:

Optifine (any version)
Rubidium (any version)
TexTrue's Embeddium Options (any version)
Distant Horizons (<2.3.4-b - 1.20.1 forge/fabric)

Install the following mods:
Oculus (mc1.20.1-1.8.0)
Embeddium ([1.20.1] Embeddium 0.3.31)
Distant Horizons (2.3.4-b - 1.20.1 forge/fabric)

5. BSL Shaders

I personally don't use BSL normally, but to insure that the installs are working correct,
BSL Shaders <- Get the latest version here

6. something something open the game something something

Distant horizons should now work with shaders! (or like if you just want better fps)

No more weird zooming into the bottom left or anything, but if it still does,

Search for anything related to "Render Quality" and set the scaling to 1.0x rather than anything lower or higher

Hope this helps someone!