I'm not sure if this is some on my side, but with this PR I have the following behaviour (when having a 3D object selected and dragging the cursor (LMB) over another object, and not being near the gizmo):

Select Mode: Selected object gets translated in viewport space
Select Mode, with Alt pressed: Nothing

Move Mode: Selected object gets translated in viewport space
Move Mode, with Alt pressed: The same

Rotate Mode: Selected object gets translated(!) in viewport space
Rotate Mode, with Alt pressed: Selected object gets rotated in viewport space

Scale Mode: Selected object gets translated(!) in viewport space
Scale Mode, with Alt pressed: Selected object gets scaled (local space)

What I would have expected:

Select Mode: Nothing
Select Mode, with Alt pressed: Selected object gets translated in viewport space

Move Mode: Nothing
Move Mode, with Alt pressed: Selected object gets translated in viewport space

Rotate Mode: Nothing
Rotate Mode, with Alt pressed: Selected object gets rotated in viewport space

Scale Mode: Nothing
Scale Mode, with Alt pressed: Selected object gets scaled (local space)

Interesting enough when I do Alt+RMB, the other objects gets selected.

I just pushed a change that should resolve that. It looks like even in 4.2 stable in select mode when you drag over some kind of geometry it will translate the node(s), which I don't fully understand why that would be the case. The changes I just made make it so it always defaults to region select.

Indeed, now everything behaves like I'd expect it to, at least in my limited test scene. Thanks!

Good to hear. Assuming there isn't any more bugs, the only thing left to finish this draft is to update the tooltips, but I'm not sure that's worth doing unless this gets more traction and because of a potential issue I found related to the tooltips: #87924

For future reference I'd suggest just rebasing your branches on top of some other fix if you want to include it, makes it much easier to rebase after the other PR has been merged, now you need to potentially handle merge conflicts

My heart is in the right place, but you're always there to make it right. Thanks again.