I have a WordPress website, unfortunately the postmeta table size is increased to 25 GB, I was storing base 64 encoded images in the postmeta table as well
In order to reduce postmeta table size, I have run a script and stored images in directory and replace the base 64 meta value with one liner image URL. I was expecting the postmeta table size to be reduced which is almost the same. base 64 encoded string is a long string of KBs whereas the one line URL is just of bytes but still no significant difference in postmeta table size.
You should reorganize the table storage to reclaim the storage space and optimize the data structure: https://dev.mysql.com/doc/refman/8.0/en/optimize-table.html