Since Mac OS 11 Big Sur release Apple allows installation of kext drivers in the Recovery mode only. It also prohibits installation of kext drivers from Apple store. Which I guess is the end of macFuse, at least for virtual/cloud file systems. What would be the migration path and how to build virtual file systems for Mac OS 11+, in particular for document management and cloud storage, similar to OneDrive, DropBox, etc.
I can also guess that a similar issue may appear on Windows too. I can imagine that Microsoft will follow Apple's path and will prohibit file system drivers and filters on Windows for these purposes in future releases. Any hint for future migration if such a situation happens would be appreciated.
Since macOS 11, Apple has updated documentation of the File Provider API which can be used to sync files between client and server and may serve as a replacement for file system drivers. Until this day Apple has not officially announced that functionality on macOS. The API is similar to the File Provider API that Apple has provided for iOS 11 some time ago but still it has some differences in mostly how main FileProvider class extension works and which abilities it has. There is no examples at this moment that I’ve seen but it looks like this functionality works at least on basic level. Based on what people say on the forums.
On Windows, Microsoft has introduced the Cloud Storage Provider (Cloud Sync Engine) API for Windows 10 in the year 2018 (Windows Creators update). It is used in One Drive for Windows. Here are some examples on GitHub in C++ and in C#.