Those have an inherent amount of pressure so that when the weight of the awning is on it, it will still "open" under that weight.
To compress it, so you can mount it, appears to be the issue.
You are left with a brute force type of thing to figure out how to compress.
My guy says Stabilus pistons are nitrogen filled, and some models have a button that's a lock button (so look for that).
Note that there's no re-filling these things so you'll have to manually compress somehow.
Manufacturer website:
https://www.stabilus.com/
However, it appears you have a older item.