Do landings have to be on the online server for them to count towards the required landings, or can they be in solo mode? Anything else I should know?
Yes they must be on the server
Also keep on mind that you can only have one landing every 30 seconds, so a bounce on landing is not 2 landings (unless ofc you glided for 30 seconds)
To kind of expand on this, only the main gear need to touch. So if you’re in the Xcub, only the two main tires need to touch the runway. If you’re in a A350, only the mains need to touch. Nosewheel/tailwheel touchdown is not necessary.
And then yes, the 30 second as Felix made mention of. Solo mode will not count. Casual, Training, or Expert Servers are the applicable servers where landings can count. Other than that, you should be set! Just don’t crash! 😜
And I assume it also has to touchdown on a valid runway?
Yup! Taxiway or terrain landings aren’t counted.
You can, however, land on a certified/charted grass or dirt runway, at airports that have them, and it would count.
It cannot be in solo mode, only online. It can be in any server. Taxiway/off-runway landings don’t count, only on runways.