Crash on Mojang screen at startup, have already updated Java and reinstalled Minecraft. Log reads-
[18:48:20] [Client thread/ERROR]: Failed to load Realms module: Realms incompatible. Built for Minecraft version 1.14.2, trying to load in 1.14.3 Pre-Release 1. Note that the realms plugin isn't forwards compatible any longer.
If your game did crash, please create a new issue with the full crash report as the error you provide is just a message that your version doesn't support realms.