I agree, it's a great UI in terms of speed and no JS, but it's not super intuitive and not helped by the way it's been split into modules.
Basically, each subdomain (git.sr.ht, todo.sr.ht etc) doesn't link to the others - the only one that links everywhere is the root "sr.ht". You can think of sr.ht as a "hub" that links to the others. So - to take an example:
- You can open "tickets" (todo.sr.ht) from https://sr.ht/~delthas/senpai/
- But - if you click on "source" (git.sr.ht), the references to the other pages anymore (including back to the hub)
So, in your case, if you replace git.sr.ht with just sr.ht in the URL, it should take you back to the "hub" for that project. Then, if the tickets feature is enabled, you should see a link to "tickets" there.