No maximum value for MAX_STORAGE_SIZE_MB is documented
No maximum value for MAXSTORAGESIZEMB is documented.
In Azure SQL Database, any attempt to set the value of MAXSTORAGESIZEMB higher than 10240 results in the following error message: "Cannot set Query Store maxstoragesize_mb to nnnnn. The maximum allowed limit is 10240 MB." This limit does not appear to be documented.