I wrote a fairly detailed report of a T280 peaceful OCC win using China a while ago. This is in Gathering Storm but several updates ago, still most of it is relevant to the current patch:
https://forums.civfanatics.com/threads/occ-one-city-challenge.656093/
Any Civ can win OCC but I like China a lot because you have a very good chance of grabbing lots of early wonders like Oracle, Temple of Artemis, and Great Library with their special ability. The basic way to win is to crank out some nice early wonders, carefully plan all your districts and improvements very early to maximize efficiency (since you only have 36 tiles to work with, and some may be lost to water or mountains), befriend all the AIs, make sure to grab Kilwa and Oxford, and use spies to sabotage enemy Spaceports and protect your own. Cross-Cultural Dialogue is a great way to boost your science. In my game I used the old Work Ethic for 30% production boost, but now it would only be like 6 extra production because of the rework. Feed the World or Choral Music might be better choices nowadays.
Not 100% sure about Pyramids being that great. It will result indoor Builders contributing 12% instead of 10% to projects (or 14% instead of 12% with China), but in OCC you have plenty of time for each space project because tech is so slow. So, this would maybe help cut a turn off Exoplanet or Lasers at the most considering your base production should be huge with a city close to 30 population. Still might be worth it with China since you can just rush it with Builders, but with any other Civ I would invest the 220h in other things.
I managed to get up to 681.3spt on the last turn:
15 from 30 population (0.5 per citizen base)
30 from Pingula (1.0 per citizen bonus)
2 from Palace
6 from Science City State bonus (x3) to capital
6 from Campus (3 adjacency, doubled by Five Year Plan policy)
40 from Campus buildings (14 base, doubled by Rationalism, and +12 from three City States)
10 from tiles (rainforests boosted with +1s by Zoo)
6 from citizens assigned to buildings in Campus
12 from Trade Routes (boosted by Merchant Confederation and Science Alliance)
51.9 from Campus Research Grants
All these yields total 180.9spt and are assigned to the capital and boosted an additional 90%
+10% from happiness
+15% from Pingula
+15% from Geneva Suzerain bonus
+20% from Oxford
+30% from Kilwa
The modified total is 343.8spt
Cross-cultural Dialogue adds 77.7 and Raj add 18 - these are considered global and not part of the city and bring the total to 438.4spt.
Finally, we add a bonus of 45% from International Space Agency with Suzerain of 9 city states and a bonus of 10% from having a level 3 Research Alliance for the total of 681.3spt.
In this example I was lucky to have 3 science city states. I formed rings of Warriors around them so they could not be killed, since I was playing totally peaceful and could not declare to free them if conquered. Three other city states were killed, did not have enough units to cover them all. Note since the patch the city states would be slightly more useful by providing +1 to library+ capital, +2 to university, and +3 to research lab for a total of +19 instead of +12. Also, the Diplomatic Quarter did not exist yet when I played this one and could provide a bunch more science with consulate and chancery.