Note: I don’t know any code or literally anything on what to do. Speak to me like I am a child.

20.06 16:48:56 [Server] main/WARN @mixin target net/minecraft/class_3898$class_3208 is public in fabric-networking-api-v1.mixins.json:accessor.EntityTrackerAccessor and should be specified in value
20.06 16:49:00 [Server] main/WARN Error loading class: org/jetbrains/annotations/ApiStatus$ScheduledForRemoval (java.lang.ClassNotFoundException: org/jetbrains/annotations/ApiStatus$ScheduledForRemoval)

Can you give the entire log?
If you haven't started the server since, it'll be in logs/latest.log on your FTP section.

If you don't post the log or the crash report, people can't help you.

@rayduit Log please?
Go to FTP/logs/latest.log. If this issue is solved, then close the issue with the Close button at the bottom of the page.

Don't think the submitter will take care of the issue any more after the initial report, and can't help hence.