can i collapse just three or four tracks or do I have to collapse everything but the current track?
There is the toggle at the bottom left of the pattern editor but this either toggles collapsing of all tracks but the current or no collapsing at all.
Collapse/Expand Track Ctrl+Shift+K
Collapse/Expand Group Ctrl+Shift+J
All Tracks and All Tracks In Group exist but have no default shortcut (I like leaving the actual group expanded but collapsing the tracks inside it personally.)