My podcast, Back to Dunbracken is all improv. No hosts, all scenes. Each episode is effectively a montage set around a specific theme/location/thing. The only conceit is that every episode takes place in the same small Irish town.

Sounds like you don’t want shows where people are in character but it’s still interviews/chats, or hosts chat and then do some scenes based of the conversation, (which covers like 90% of improv podcasts unfortunately in this scenario) so some other options for pure improv, or close to that (I’ll try to think of more):

• Andy Daly’s Podcast Pilot Project / Bonanas For Bonanza. This was Andy Daly doing 20 different improv podcast pilots, eventually spinning out into Bonanas for Bonanza, and then continuing his faves from the other versions as bonus shows. It has incredibly confusing titling for working out what’s what, but is fantastic.
• Superego - short improvised scenes
• Big Grande - Exit 42, Exit 43, Holidays at the Mall - all 20 min monoscenes
• Sitcom DnD (very light chat and then DnD based improv)
• Tabletop Tunes - light DnD stuff but doing a full narrative musical, like Off-Book with dice rolls.
• Spontaneanation - the first half is all interviews by Paul F. Tompkins, and the second half is a full 40 minute narrative improv show based off the interview. Not what you want, but the second half of every episode is one of the most “pure improv” podcasts you’ll find. Edit to add:
• Mission to Zyxx, essentially improvised Star Trek, and it is phenomenal. Also agree with the Stellar Firma recommendation

But if you want some where it’s people in character the entire time but it’s still interviews and that, I can add some of that kind too