I've been getting the "Failed attempting to join realm. Please try again later." message a large majority of the time I try to connect to my friends realm. I just got the message 3-4 times in a row in the last five minutes, 19:08 PDT 04/22/2020. I run into the message a handful of times nearly each day.
I can provide realm name and Gamertag of realm owner.
We are not able to provide direct support through the bug tracker, if the problem is with only a specific Realm, you, or the realm owner, will need to contact Mojang Customer Support.
First though you might look at: Realms FAQs - Connection Issues
You might also try the Minecraft Community Support Discord at: https://discord.gg/58Sxm23