Whu were you expecting a spinoff to last long? even the previous spinoff ran for a short time.lol wow this was a sudden axe! Have to say, it's prob been my least favorite shoujo isekai I've read, but it felt like it was at least going somewhere? Global Manga+ is a chapter behind, so it looks like the next/last ch will be out Aug 12th. I'm guessing "rushed ending" over "time skip" or "the journey continues".
Kira Etō's World's End Harem ~Britannia Lumiére~ Manga Ends
Spinoff manga launched in June 2020, went on hiatus from December 2020 to June 2021 due to author's healthwww.animenewsnetwork.com
Just continue the main series.