There is a third party package that provides polymorphic relationships, adonis-lucid-polymorphic. I’m not sure if it actually works, it didn’t seem to last time I looked at it (several weeks ago).
You could use an Exclusive Arc table, rather than a polymophic pivot. Not sure exactly how, or if, it works outside of postgres.
The easiest, and probably most performant, option is to just create several pivot tables & many:many relationships for each thing you’d otherwise polymorph.
So say you have
videos, catgories & posts have a many:many relationship as for videos & categories.
You would create your categories, post and videos tables as normal, then create individual pivot tables;
This introduces more tables into the DB, but it’s a much more performant join than having to match a foreign table name and an id as is necessary for polymorphic joins.