If it is clearly said yes in the rules, what it isn't, you can't use it.

I'm pretty sure its allowed since the runs are labelled under the creator of sodium.

Awesome I'll see if I can get a few more responses before I use it in a run

This is what is stated in the official mod rules:

Mod Rules
Optifine is allowed for versions 1.0 through 1.15
Fabric, Sodium, Lithium, and Phosphor are allowed for 1.16+
If you use Optifine, please read the detailed mod rules at http://bombch.us/DOOK
All other mods are banned

@UnSyncUnSync Thank you, I didn't see that in the rules

So you can use Optifine in 1.16+ as long as you keep to the mod rules in that link?

Optifine is not allowed for 1.16+