As of January 2023, Spotify is rolling out a new player on iOS and Android mobile apps that includes chapters.
To use this feature, you can add clickable timestamps in the episode description. If you've ever done this with YouTube it's a very similar system.
At this time, Spotify isn’t supporting either ID3 embedded chapters or chapters via the new podcast tag "podcast:chapters", so for chapters to appear on your podcast on Spotify you'll need to use their internal system.
Here's Spotify's help article on how to add chapter links.
Note: Timestamps are currently only clickable on mobile.