only watch "The Frozen Bond"
ReZero kara Hajimeru Isekai Seikatsu OVAs

you should watch Ousama Ranking Yuuki no Takarabako, some stories are worth watching especially in the second half of the show and the last episode is canon, continuing where the first season ended

when you get back to Golden Kamui, don't forget to watch the OVAs they're all canon and cover skipped chapters/arcs