The version you are using is highly bugged and not stable. Within days of release of this version the download page was changed to suggest the prior version 21.03.21 to be used in it’s place.
It might be possible to salvage your project file you just upload the MLT here. No guarantees though.
If you have moved media files from their original locations this will cause the INVALID screens to pop up. Read here (scroll to Missing Files) on how to fix this situation.
When exporting it may stay at 0% for a while as this is normal as Shotcut tries to estimate a remaining time. It’s not highly accurate, but as the export happens the time get’s more and more accurate. If you’re exporting to a HDD (Hard Disk Drive) vs. a SSD (Solid State Drive), then it may take even longer at 0%. You didn’t state any length of time that you waited. It’s also known that certain anti-virus programs can and do block Shotcut’s export program.