cupiditys

Please check out this article: https://help.minecraft.net/hc/en-us/articles/360029643892-Can-only-play-Minecraft-demo-Java-Edition-

If that doesn't help, please contact Mojang Support.

This is intentional, if you'd like to respawn simply press the respawn button? Pressing title screen and exiting will save the death status so when you rejoin you are still dead.

It seems to be crashing after failing to connect to Realms. You should ensure you have a strong connection, re-login, or restart your computer.