ENT era.

Externally speaking Starfleet ships march to the beats of NACA/NASA X-planes, Klingon embrace a very soviet yet alien look in contrast, Vulcans look advanced and sleek yet ancient and mythical with the biggest pointiest toys on the block.

Internally speaking construction is depicted as having limits, tech and interfaces are familiar to real world, cramped ship like rooms are the norm, and there’s no handwaving over how everything might fit inside the ships.

The automated repair station from ENT’s Dead Stop (AKA The Ware) The novels presented an interesting idea of these rogue clumps of machine learning forming symbiotic relationships with sentient life that have the developed grey matter the Ware needs, but are filtered from becoming advanced, tool using, space fairing civilizations due to essentially lack the physiology like the opposable thumbs common to progenitor seeded humanoid races.

Xindi showed up in the later half of PRO. They ran security at a seedy trade hub the kids were trying to hitch hike from. The thing was though that these were Xindi Reptilians and this was a snowy Ice world… Kinda a problem when ENT dedicated screen time to saying Reptilians were cold blooded (though to be fair Reptilian’s did have an inclination to bio-engineering they could have just made themselves warm blooded).