Hi there, first up, don't be shy about asking these questions as it helps the community.
To add my 2c, I think it varies from startup to startup. We have followed quite a rigorous screening for our startup and have never been disappointed with the choices we've made.
We were doing a rigorous HR screening, followed by 1-2 phone calls with Senior engineers, finally bringing the candidate in for 3-4 hours of discussions with various members, including Senior leadership.
This has all moved online though but our process has been unchanged and it has gotten better as the interviewers have adapted to dealing with a wide variety of candidates.
Sometimes, we split the interviews over 2 days to give the candidate breathing room and also allow flexibility in scheduling.
The interviews with, and feedback from, senior leadership has especially been helpful to decide and settle on the competent candidates so we never had to regret our decisions.
Hope that helps!