I learned at SQL Server on Windows the Allocation Unit Size (sector size) must be 64K because of the pages.
It doesn't have to be 64k, in fact you'll generally get the best performance based on your workload and the storage vendor's preferred size. If you don't know either, generally 64k will be used.
Is this also required for the SQL Server on Linux and if yes is this supported on ext4?
It's not a requirement. If you can do testing ahead of time and figure out the sweet spot for your hardware and workload, then that would be the best. Most of the time, the performance difference is negligible unless there truly is a bad configuration for the hardware or workload.
At the system requirements on the docs of Microsoft is only the information of which file system but not more details.
That's because it isn't required. You can use whatever you'd like, but if you truly wanted to find the proper value - testing is required.