Solved! Go to Solution.
Apparently I can't mark my own post as the accepted solution. Do you mind trying? On your phone you can click the three vertical dots across from my name on that post. "Accepted solution" should be an option. Thanks.
I had the same problem with Secure Folder version 1.8.01.5. Using the Google Play Store, I was able to look up Secure Folder and uninstall all updates to the app (can't completely uninstall because it is a system app). After uninstalling updates, I was reverted to version 1.8.00.41, and Secure Folder now works! No more app crashing. Interestingly, after reverting to 1.8.00.41, searching the Google Play Store, Galaxy Store, and "About" section in the Secure Folder app all show 1.8.00.41 as being up-to-date/ the current version! My guess is that 1.8.01.5 was broken and caused these crashes, so they pulled the update, but failed to roll back that update for anyone who already updated. At least it's working now.