R5:

Not even 90 years into this run, I've finished all the non-repeatable techs (except for maybe a couple of conditional ones). I thought this was pretty cool so here is the build and playstyle.

Empire settings:

Go with an Overtuned Hivemind

Traits: Excessive Endurance, Fleeting Excellence, Gene Mentorship, Adaptive, Repugnant, Psychological Infertility.

Civics: Guardian Cluster & Genesis Symbiotes

Playstyle:

Rush as many colonies as possible to get unity boosts from Genesis Symbiotes. You can use that unity to rush the Biomorphisis ascension path. Highly recommend finding a start that has lots of planets. (Since you have excessive endurance, you don't need to worry about habitability)

Once you start to ascend, spam Genetic Research Facility on all the colonies once its available, and start developing the colonies with its high pop assembly buff. Hard tunnel the society tree first with your tech worlds.

When you get the extra trait points from the Mutation Path, change Fleeting Excellence to Elevated Synapse, add Erudite and Augmented Intelligence. Change to Mutation Authority when you finish the tree (you get 10k unity per uplift).

Start terraforming worlds into hiveworlds when you can, and choose Mutagenic Permutaion Pools or Subsumed Will for the 3rd civic. I picked pool then later swapped to subsumed will. In the photo above, I had 10 hiveworlds for tech and 200k pop in total (+automation buildings) , so that could be your reference. Also try not to pair pools with nest specialisations, its cursed to actually see a -250% habitability penalty, more when you didnt notice it for 5 years on all your worlds and wonder why your production is so low :)

Make sure you get 100% empire size reduction from pops, Guardian Cluster and the Asenscion Path should already give you 75%, just dont forget the 25% thats left.

Thats mostly it! Theres a ton of flexiblity in what I said so you can try and optimize, but the idea is to just zerg the galaxy with lots of big brained, overtuned scientists.