Do you mean you are not able to enable the flexible option? The picture is not that much clear but still flexible options seems OK.
Can you click on the flexible option? Can you close your files, reopen and check them once again. Try force rebuilding (ctrl + Q) and check.
Lastly, can you share the files to check?
The Flexible option is only for allowing movement of a sub-assembly within an assembly, not movement of an individual part. If you do a search here for "animate a spring" you will find several previous posts. The video link in one of Deepak's posts (the second post in this discussion) was partucularly helpful to me on a project I had a few months ago.
Did you get it to work?