We're not seeing any widespread issues at this time. Can you let us know what troubleshooting you've already tried, and what platform/version of Minecraft you're playing on? ^FF

i second this @MojangSupport im unable to join any realms on java edition

Are you encountering any errors, and can you let us know what troubleshooting steps you've tried so far, if any? ^FF

restarting my client and pc. judging by other tweets ive seen this seems to be an issue on your end