Although I am using Bootcamp Windows 10 on a Mac, this is an issue for several people I know. I play on a PC, while other friends use an Xbox 1s to run Minecraft. As soon as the 1.17 update has been released, whenever I would try to join his world (that we made prior to 1.17) It would say "connecting to multiplayer world" and stay on that screen for a solid 30 seconds, before saying "unable to connect to world" This however, is not the case for worlds that have been created within the update. We have created worlds in the update and have had no issues connecting with each other. In conclusion, there seems to be a lot of multiplayer bugs for many people. Within the next hotfix, many would highly appreciate if multiplayer bugs could be sought out and removed.