Confusion about HA , LOG backups and availability
1) Availability Groups are in sync with it's replicas by log files, right? So the primary replica sends information from the LOG files to the secondary.


Looking at it form a very high level, yes.


  2) With log shipping, I need a job to backup log from primary, copy it to another drive, send it to the netword, and then another job in the secondary replica to restore this log into the database. 


You do'nt have to necessarily copy it/move it, etc., if you take the backup to a place that is already shared with all other log shipping partners. The overall steps, though, are the gist.


  I dont need this naymore with Availability groups right? Primary replica already sends log data directly from the log file to the secondary replica. Or is this wrong?


Very high level, you're correct.


  3) I ran a query and I noticed that there aren't backups in this server ( primary) since 2017, and logs since 2018. Is this a problem for Availability groups?


It's a problem in general. Should you need to restore from a backup, there aren't any recent ones. Since the logs haven't been backed up, their log files will continue to grow until they max out or the disk is filled, whichever comes first.


  with no log backup files, there's no information to send to the replica. Or 2) is right already?


The log is transmitted regardless of backup activities.