it demands fabric 12 or 0.8.0 when (in the launcher I'm using) we're at about 40.

Downgrading Architectury to 1.5.112 allowed Optifine to work.

My version runs matching your versions @topia; however, it is not working using Architectury (1.32.66)

The most recent one shown by curseforge

View files > select version > 1.16.5

I do not know what that is

There's no necessary information to resolve this issue because I confirmed optifabric 1.13.16 on Minecraft 1.16.5/fabric.
Why do you think it doesn't work? Could you check the latest log? What mods (and versions) did you use together?

What version of optifabric are you using?
I confirmed I could launch with 1.16.5 fabric.

- fabric-api-0.42.0+1.16
- optifabric-1.13.16
- OptiFine_1.16.5_HD_U_G8
and:
- fabric-loader 0.14.12

I opened the game again and now it works 90 or so hours later with no changes but sudo apt update. I am sorry for wasting your time