this error is present since the early 20th but that doesn’t help you.
MariaDB und mySQL share the same join table limit.
I personally never hit that error message. Take a brief look at the SQL-Statement (or post it here, somewhat obfuscated to protect your privacy)
Try disabling some of your addons in a development environment and try again.
I deactivated all the plugins and checked again and still the issue repeated.
But the funny part is, later I noticed that the value get saved even if the error message comes up (So for now I can continue with the heavy workload).
There is no custom code running on the application so far I know.
No suspicious error message shown on the Shopware error log.
I will probably come back with more information after a closer look.