I tried swapping running with cycling for a few months but honestly as somebody who spends a good portion of my time on my ass, often with suboptimal posture in front of a screen I hate the idea of exercising still sitting on my ass with bad posture.

The most important thing imo is to find a form of cardio you enjoy. It's not worth stressing over the differences between forms of cardio just find something you like and make it a part of your lifestyle.

Reagarding knee injuries, sure intense running with bad form is more likely to get you an overuse injury but those heal quickly, long term studies don't show increased knee/hip risk for runners.

Strength exercises are also very important for runners. Getting all the muscles arounf your hips, knees and ankles stronger significantly reduces the chance and severity of injuries and has a ton of other benefits.

If you are sitting on your ass (as in the normal definition of buttocks) when cycling, you are doing it wrong or you are riding a recumbent.

Typically you sit on the part in front of your hip, which also has its downsides as it is quite a delicate area where pressions on the wrong area could lead to issues.

MTB is the solution here. You can't really sit down when it gets a bit rough.