Shortcut inquiry for "T" as trimming the main timeline w/o moving sub timeline

Since you've helped me greatly with my recent request, I'll try again.

I've heard about it, but can't remember where and how to describe the function. Therefore "googling" isn't an option, really.

The main timeline - the magnetic one - is called timeline, right? So once I stack clips on top of it, those tracks are called "sub timeline"? Anyway, when using the "T" option to trim the clip on the main timeline, all the stacked clips on top of it move with it.
You feel me? what's the keyboard shortcut for the function to still trim the main timeline without interfering with the stacked clips?

Your help is highly appreciated, as always.

The window pane is the Timeline window pane. You open a Project into that pane to edit it. The dark main track-like thing is called the Primary Storyline.

Stacked tracks are called Connected Clips, which connect to clips in the Primary Storyline via their Connection Stem.

You can change the location of the Connection Stem by holding both OPT and CMD together while clicking on a Connected Clip where you'd like to move the Connection Stem to.

T activates the Trim tool and gives you access to all trim operations.
A activates the Select too, or as I call it, the Arrow tool, and only gives you access to ripple edits operations.

The Tilde key ~ (or Grave key `) at the top left of your keyboard, when held during edit operations, overrides clip connections, so that Connected Clips don't move during said editing operations.

droeder wrote: ...The main timeline - the magnetic one - is called timeline, right? So once I stack clips on top of it, those tracks are called "sub timeline"?...

Besides what Ben said, the connected clips can be either independent or group into a "secondary storyline" by selecting them and doing CMD+G. For more info see the FCP docs. The entire FCP user guide is available free on the Apple book store:https://books.apple.com/us/book/final-cut-pro-user-guide/id976299089

See the free 60-sec Ripple Training "Quick Tips, Vol 1":  www.rippletraining.com/blog/final-cut-pr...quick-tips-volume-1/

Vol 2:  www.rippletraining.com/blog/final-cut-pr...quick-tips-volume-2/

Vol 3:  www.rippletraining.com/blog/final-cut-pr...-quicktips-volume-3/

Vol 4:  www.rippletraining.com/blog/final-cut-pr...-quicktips-volume-4/

Vol 5:  www.rippletraining.com/blog/final-cut-pr...-quicktips-volume-5/

Additional free tutorials:  www.youtube.com/channel/UCOE_zSaeU1xd9yIk6kfwf_A

And online here.
support.apple.com/guide/final-cut-pro/welcome/mac

This might be what you are looking for...

Move Main Timeline Clips Without Moving Layers [FINAL CUT PRO TUTORIAL]