@tomh :
I haven't used JotForm, so I can't test possible solutions but I would like to make one suggestion. It is possible that the date string provided by JotForm doesn't look like a date to Flow so i isn't presented as an option.. You might try creating a string variable. Initialize or set the string variable using the formatDateTime expression and feed it the Submission Date from JotForm as the timestamp. Then reference the variable when you are populating the SharePoint list.
You might try similar techniques for other columns that you can't seem to reference.
Also, I am assuming that you have already clicked on "more" if you see it in Dynamic properties and the column you want to reference still doesn't show.
It's worth a try...
If this addresses your issue, please mark your post as Solved.
Scott