Sandisk doesn't specify. (Ultra microSD UHS-I CARD | SanDisk) The answer would depend on exactly what sort of NAND Flash was used.
But I think the question you're asking is "How many times a cell can be written to before it becomes unusable?"
The answer for the sort of flash used these days is "about 10,000" And the drive firmware attempts to distribute writes evenly across the drive. So the bigger question is "How long will it take for any individual cell to to be wriiten to 10,000 times?" The answer for normal usage is that you'll be replacing the drive with something larger/faster long before you notice drive ware.
They definitely do have "drive firmware". One of the huge problems with buying larger microSD's on Amazon is there are "pop-up" vendors that buy 8 or 16GB microSDs and reprogram the firmware to show a huge size like 128GB or 256GB, then they sell them at extremely low prices.
When the buyer accesses the partition it shows a large size and for awhile everything seems to work. But as they continue trying to put data on the drive they start finding either that other stuff is getting lost or they're getting "defective disk" errors, etc. By that time the time to return it has expired.
And the person behind the "company" has already created 4-5 new "companies" selling on Amazon.