Hello,
I’m running a MySQL 8.0.28, which has a master and a slave, and the Xtrabackup v. 8.0.35-30. The backups are being performed on the slave. The problem is that while the backup is being made, the replication seems to stop, causing a high value for seconds behind master. I have others environments with the same versions, running the exact same backup script and this behavior does not occur on them.
Also, if you can share the xtrabackup command you are using for taking backups, it will help us understand what may cause the issue with replication being stuck.