⊙ A7's Clip Library directory is '~/.local/share/sounds/clips'.

⊙ A7 is not set to scan ~/.vst or ~/.vst3.

⊙ A7 reveals an issue on Ubuntu re limits.conf, reporting that memlock was set inadequately, even though the pipewire group is set unlimited automatically and I set the audio group unlimited by hand.
To get memlock set right you have to be very specific in limits.conf:

@audio          hard    memlock     unlimited
@audio          soft    memlock     unlimited

and on general principles carry that syntax over to realtime priority:

@audio          hard    rtprio          95
@audio          soft    rtprio          95

⊙ Ardour - how to use MIDI sequencer with mouse

Add synth to track
Choose sound (double click on instrument in mixer)
Choose pencil
Click in first bar (anywhere) to create a region
Choose Move tool
Drag to start of track
Stretch to right (to the end of bar)
Choose pencil
Hold mouse alongside virtual keyboard
Drag mouse to right to get required length of note
Press Esc [??]
(To move note, use pencil, click-drag note to required place)
(To lengthen note, use pencil, drag end to required length)
(To loop range, select range tool, select Grid snapping {if needed to be precise}, click-drag from near left of range to near right of range - grid snapping will complete the range)
Right click on range –> Loop Range
Can press "L", once Loop Range has been set
To copy range –> range tool, select range (part of region or all of region), copy, move mouse to required location, paste
To copy region –> grab tool, click on a range, copy, move mouse to require location, paste
To unlink a region –> (with grab tool) copy and paste a region –> click on new region, go to Region menu at top of screen –> MIDI –> Unlink from other copies

⊙ Ardour can't undo-redo adding tracks. Adobe Audition 1.5's multitrack view gives you 128 tracks off the bat; possibly you can't have more, I'd have to check the manual, but maybe a default template for Ardour should be 128 tracks?