enable content logs and then try to open the the worlds. Then go to 'C:\Users\USERNAME\AppData\Local\Packages\Microsoft.MinecraftUWP_8wekyb3d8bbwe\LocalState\logsThere should be the logs. Pls send it to me
As far as I know, there is no such thing as Optifine. I think there are two possibilities with shaders. Either you have an RTX graphics card with which you can then play RTX shader packages like Vanilla RTX or you look for shaders on MCPEDl. Also for things like Bedtter Dogs I would recommend looking on MCPEDL for what you want.
I don't know how it is on the switch, but I play Minecraft Bedrock on the PC. No worlds should actually be deleted, but I can't say anything about the Switch because I don't have one. Maybe someone who has a Switch and knows will answer. But my opinion is that if you don't have to reinstall Minecraft somehow when you switch accounts, the worlds shouldn't be deleted.
Go to your Nintendo Switch settings> Internet > Internet settings > click on your wifi > Change settings > Change DNS settings to Manual > Enter as Primary DNS address: 104.238.130.180 > And for Secondary DNS address: 8.8.8.8 > Then click on Save > Restart Minecraft > Log in normally > go to Server and wait until at least one has completely loaded and go to that > Then a window should open where you can choose the IP address and port of the server. When it doesn't show the window try it again.