I understand why on the surface it could feel like filler, since is was essentially a side quest with Loki and Sylvie. But that totally makes sense to me - they JUST introduced the Sylvie/Loki character, who is obviously a main character in the show. Not only do we the audience not know her, but Loki doesn’t either.

And even with that, this wasn’t just a character development episode - Loki and Sylvie needed this time to work together and build trust. I don’t think that’s an accident - Loki seemed WAY less pressed than her about getting off that planet, so I think he set up this whole situation as a trick so he could get to know her and find out information. He probably got drunk on purpose to get thrown off the train, then when they were running towards the ship he was telling her to slow down. He probably has that time device or whatever perfectly functional (or maybe he stole one of the time stones from the drawer at the TVA) so he can get them out as soon as he gets the info he wants.

On top of all that, we got the huge reveal that all the TVA agents are variants. There were hints that the Time Keepers were really the villains all along, but now this is laying it all out there. Mobius is probably some guy from the 90’s who used to sell jet skis or something. This also goes back to when he was in the judge’s office talking about the “other agent”. That might be another variant Mobius. I remember him saying something about not remembering putting the rings on her table.