I reached out to support and they told me to follow the steps of deleting game save files for Steam and try again, unfortunately I had to say goodbye to my progress, logbook etc (There’s also a guide to delete progress for MS store.)… Third party software and community folder was not my issue as it turns out…
It worked! no more CTD’s when clicking “ready to fly”. The detailed progress was lost tho (ie: logbook), but the overall achievement is still there (ie: before this my next milestone was 50 hours, now my next milestone is 100 hours…) but the progress bar is empty.
Now I’m just wondering how do I restore the full progress.