Kamen Rider Build

Both Kamen Rider series feature an amnesiac Rider who is 'adopted' by the family of the heroine (which has powers). There are also four main Riders.

Adachi's actor (Eiji Akaso) plays a hot-headed former boxer that was framed for murder that slowly and awkwardly gains feelings for the protagonist. Sorta like kurosawa does

Both shows have the main hero fight of terrorists at first. Later they become involved in a big corporation/governmental competition. It has multiple rider fractions and rider-like fighters.

Zi-O is series following Build so if you want to watch the Kamen Rider seasons in order than you should watch Zi-O after Build

Build is the series following Ex-Aid so if you want to watch the Kamen Rider seasons in order then watch Build after Ex-Aid.

"Tradition. History. Pride. Struggle. Reflection. Courage. Beyond that, there is innovation. Don't lose your dream.

Wake up."

In a world shaped by the dreams we see in our sleep, ZEZTZ enters people’s dreams as an agent on a mission. Equipped with a cutting-edge Rider belt worn across the chest, ZEZTZ brings a bold new form to the battle.

Both are contemporary hero shows, that aired around the same time, focusing on a pair of characters - the Minato brothers in R/B and the "best match" guys in Build.
There are also fourth wall breaking "previously on" segments for both shows.

The biggest difference, at least in my opinion, is that Ultraman R/B has multiple, actually well-written female characters. (And it also does not have a 29-year-old man/19-year-old woman relationship.)

Build comes before the 20th Heisei anniversary

W comes after the 10th Heisei anniversary

both have dual colored riders

both have an ultimate form accessed by rider fusion