I have a realm on bedrock edition on Xbox series S with 3 add-on (furniture by xp games, gravestone by darkosto and spark portal by spark universe). Since 1 week i have extrem lag on my realm. I make the update 1.21.20 and no amelioration. It's not dependant of the membres because even at 3 membres same result.
Before 1.21.20 you would have thought it depended on the time.