3rd Party Guitar Plug-Ins for GarageBand 10.4.7

When using GarageBand 10.4.7 (on M1 Mac Mini), why don't the 3rd party guitar amp sims (plug-ins) work with their gui (like it does in this video: https://youtu.be/xlreWvaQyB0).

1. Audio units is switched on.
2. Track was selected, and smart controls is open.
3. On the plug-ins, navigated to Audio Units > and picked the visible plug-in (which apparently was recognized by GarageBand as Audio Units). However, instead of the GUI for the amp sim (resembling the YouTube how to video)

there are a series of sliders that do nothing (see this)

Ultimately, I'd like to bring Overloud's TH-U into GarageBand and record with that as a plug-in. Overloud TH-U is installed and working as a stand-alone application on the M1 Mac Mini. GarageBand recognizes those Audio Units plug-ins, but doesn't pull in the GUI nor the actual amp sim sounds - weird.

What am I missing? This is supposed to be easy - it's an Apple, right?

Thanks

Eddie