Update: I took advantage of the sale and updated from Cubase Pro 10.5 to Cubase Pro 11.0. I’m now running Cubase Pro 11.0.30 on macOS Big Sur 11.4.
Sadly, the original problem remains: when I navigate to the SysEx files to import, they show up grey/disabled. So I’m still not able to select any of them for import. (Yes, I started up Cubase 11 Pro, not the old 10.5 Pro.)
Upon first start of Cubase Pro 11, I gave it all the access permissions it prompted for. Also, my user is Administrator.
Can anyone provide any additional advice as to what settings to change or check for this? It seems to be a file access problem specific to macOS (and maybe Big Sur, but I haven’t had the chance to try on macOS Catalina).
I have also updated an open MySteinberg support ticket with this information, after I got a reply from support, stating that this should work normally.