In terms of “filler” episodes…

I don’t think I would consider any of the episodes “filler”. Even Chapter 5, despite not setting anything up, provided lots of insight into world as well as just a fun adventure.

I actually find too much focus on an overarching plot a sign of a “filler episode”. Let me explain. Way too many shows focus on building mysteries and teasing the audience, to the point that’s the entire show.

A good example would be Stranger Things 3. I was bored watching most of it, and I kept wondering when the plot would actually start. Because the first 75% is just slowly teasing the ending, when I would rather they either shorten the season or add new storylines to make each episode somewhat unique.

This is why I like Mandalorian so much: each episode brings something new to the table.