How to simulate click (and hold) from top left corner of screen drag to bottom left corner (now release)?

I'm genuinely confused how to execute this, if it's possible. I want to assign a keyboard shortcut to this action (Opt+Shift+3, for instance).
I have some work which requires me to take scrollshots. I use Shottr for this. I've set up Opt+3 for scrollshots in Shottr.

My execution requirement:
Opt+3 (to enable scrollshot mode, discussed above) --> Move mouse pointer to top left of screen --> Left click AND hold --> Move/drag mouse pointer to bottom right (with left click held) --> Release click now.

Maybe this is obvious, but somehow I cannot find how to execute this.

Edit: I've tried reading multiple posts on this community, but I cannot seem to find out how it's been done.

You might be able to get it working using the "Custom Mouse Buttons / Modifiers" action and the "Move mouse to position" action:

However depending on the screenshot app this might be hard to achieve.

An easier way would be to use BTT's integrated "Capture screenshot (configurable)" action and choose the specific rect option: