As mentioned by @trieren1, you can use Boxcryptor Portable for macOS for basic file access to your encrypted files.
In general and as with every macOS (or iOS or Windows or Android) beta release, we do not recommend upgrading to beta versions of operating system on production systems. By the way, this is also Apple's, Microsoft's and Google's recommendation. If you really have to use a new beta version, you should either install it on a separate drive / partition or - even better - on a dedicated second device. As an independent developer, we also only get access to new beta versions when they are released to all developers or the public. And only then can we begin with the work to support it. Depending on the changes in the new operating system version, this can take from a few weeks to a few months. But as always in the past 9 years, we will have support for a new operating system version at the latest when the stable version is released to the public.
Nevertheless, we have created a (very) experimental version for macOS 11.0 Big Sur which contains an updated filesystem driver with preliminary support for the new OS. Besides the updated driver, this version does not contain any other adjustments for Big Sur. Therefore, it still shows the "Unsupported macOS version" message and unexpected problems might occur - from simple UI glitches to data loss. Please use at your own risk - it is not a stable version with macOS 11.0 Big Sur support.
You can download the experimental version here:
In the coming weeks we will also release improved experimental versions for Big Sur.