Hello,
Sadly, this is a browser limit and they don't want to increase it:
https://github.com/w3c/webextensions/issues/510
I plan to implement custom synchronization, but that will take some time.
Note that you can change the storage to "local" which is unlimited, but not synchronized/backed up, to other devices. See Settings / Options / Storage .
Best Regards,
Juraj Mäsiar