Question: difference between Stack Inserts and Mixer channel Inserts

Can someone tell me the difference between (1) and (3) and between (2) and (4)?

If they are the same it´s ok as we have 8 Inserts combined, if not could we have more Insert slots?
Why are there Actions to enable/disable Inserts (1) and also Quick controls but not for Inserts(3)?

Stack fx’s/inserts are self contained, like a box.

Stacks are submixers:
in (volume) → inserts →
→ send fx 1 fx2
→ out (volume)
mix out, fx1, fx2 (volume) to Stack mixer channel