Thank you... This is a known bug in Alice 2 which we are trying to address...
One workaround that seems to work for me, if you are comfortable using the Terminal on your Mac is to type in the following at your prompt:
/Applications/Alice\ 2.5.app/Contents/MacOS/JavaAppLauncher ;
This is the path to where Alice 2 is located on my computer. (Alice 2.5 is located in the Applications folder.) You may have to modify it for your own setup. You may be able to paste that line directly into the Terminal and press the Return key.
Also, in System Settings: Security & Privacy: Full Disk Access I added Alice 2 to the list. (I cannot remember if I did this before I found the Terminal command) and I am not sure that it is necessary, but it has not hurt me.
When you try to open a file through Open File, it may take a bit of time for the file open window to populate the folders and files, but they eventually show up.
I will be curious as to whether this works for you (BTW, I do not have Big Sur installed yet, but I am running Catalina). Let me know if you have any questions.
Don Slater
Alice Project
don@alice.org