I think the A380 at MAN is boarded/de-boarded via L1 on the lower deck and L2 on the upper deck (please correct me if necessary).
Yes, T3 is closed so no access to check in, security or immigration. However, Loganair, Eastern, Blue Islands and BA are using various T3 stands. On arrival passengers are directed to the T3 domestic arrivals baggage hall and exit T3 arrivals.
Some Ryanair arrivals & departures are used but the passengers are bussed to & from the aircraft from T1.
My personal opinion is that T3 check in areas are better than the cramped T1…but could do with a little spruce up.
Security is a nightmare like T1, once you have more than 2/3 Ryanair flights and only a few lanes open it’s chaotic! So the staffing levels need sorting out first to ensure adequate lanes are staffed at the peak times!
The immigration in T3 has to be the worst experience due to the small size for the number of flights & passengers it handles! I don’t know if there is an option to extend but something needs to be done urgently! Baggage reclaim is ok but again needs some TLC.
The gate areas are ok to be fair, decent enough seating at most gates and less cramped than most T1 gates!
When they finally reopen T3 it’ll probably ideal for Ryanair given their growing expansion and the fact most other airlines will be in T2 by then.