Hi! Thanks for ModMenu! In MC 1.19.4 with ModMenu 6.1.0-rc.4 it was super easy to access it, it added a "Mods" button to the main menu and the pause menu. Now I'm playing a 1.20 modpack that includes ModMenu 7.0.1, and I verified the JAR is the same as on the release page, at least they have the same SHA-512.

However, I was unable to find the Mods button anymore. I disabled all other mods to make sure it's not a conflict, but still no trace. Screenshot of my main menu.

MultiMC's "Minecraft Log" (where all the Java messages are collected) does not contain the word "ModMenu" (letter case ignored). How can I start debugging this?

Just to make sure, is Fabric loader installed in your instance? From the screenshot you've shown, it looks like the loader isn't installed so no mods are running.

Thanks for reminding me. I had assumed a mod pack that comes with lots of Farbic mods, would have included the Fabric loader. I also assumed MultiMC would have warned when using loader mods without a loder. Sorry for having wasted your time.
Update: Now with Fabric API installed (tutorial), it works as expected.