I think realms shouldn't be purchasable until this problem is fixed.
I am kind of hesitating to continue for my bedrock realms subscriptions because this has been a major problem for bedrock realms owners. I really hope this resolved very soon.
This problem has not been resolved on the switch for 1.16.4
I have had this problem too since I made this realm after the Nether Update. I am currently playing on 1.17.10 where the upload will load but "initialize upload" sitting there for 5 minutes until it realizes an error has occurred (only if you archive Minecraft on a switch). Worlds in 1.17.10 do take up quite some space, mine being around 370mb.
I am quite upset that this hasn't been completely fixed, although it was slightly worked on in 1.17.10. This world isn't caves and cliffs experimental btw.
I pay for a 2 person realm and am trying to put the same world on my 10 person realm. I'm spending a lot of money and want this to be fixed soon, as I have spent hours trying to troubleshoot.