I recently learned the game, which in the past I dreaded learning, so I didn’t bother learning it.
This sentence is not a main clause within a relative clause. It’s a compound sentence with a non-restrictive relative clause occurring after the first main clause.
It is possible to have a dependent clause within a main clause, the most common being relative adjective clauses (e.g., My brother, who lives in Ohio, is an attorney).
You can also have adverbial clause in the middle.
I finally acquired, after I had saved money for two years, the last piece in the collection.
There should be a reason for this structure, which is typically for emphasis.
The examples you give are all obvious to me, and I’m sure you know that I know these constructions you state. I don’t mean ‘within’ exactly.
What I mean is that the relative clause is needed for the next part to make sense. I didn’t bother learning it because I dreaded learning it in the past. I’ll try think of another example:
I recently went to the playground, where I broke my leg, so I cried most of the time.
This one depends more clearly on the relative clause’s existence than the first example I gave you.
See what I mean? The last main clause is sort of as a result of what is said in the relative clause (rather than the first main clause) and has nothing to do with the first main clause.