JR East is currently rolling out a new, streamlined booking portal. However, in classic Japanese style, attempting to access it from a non-Japanese IP returns a 403.
There was also news earlier this year that all the major JRs will introduce a unified booking portal in 2027, but I was unable to find any proof of life that this is actually happening.
https://go.jreast.co.jp/
There was also news earlier this year that all the major JRs will introduce a unified booking portal in 2027, but I was unable to find any proof of life that this is actually happening.