We have now opened a commercial services section here on the forum for registered users. If you have a Fabrik project that you wish to have someone work on for you, post it under Help Wanted. If you are an application developer and wish to earn some money helping others, post your details under Fabrik Application Developers.
Both of these are unmoderated. It will be up to both parties to work out the details and come to an agreement.
For running J!5.1 you must https://fabrikar.com/forums/index.php?wiki/update-from-github/ or include the new file manually https://fabrikar.com/forums/index.php?threads/joomla-5-1-and-fabrik-cannot-find-files-error.54473/post-285151 See also Announcements
When you are connected to the back end, I guess it is as Super User. Does this user assigned to the "registered" access level? Access levels are not hierachical : if adding of record is set to registered users, that means that ONLY users assigned to that level access can add records. By default, Super Users have no access right to Registered access.