By default, Proxmox (PBS) will keep all backups forever. Here is one road map on keeping your backups under control.
Garbage Collection Schedule
On the PBS server, select Datastore and the datastore you created. Now click on the “Prune and GC” tab. Double-click on the “Garbage Collection Schedule” line under the “Garbage collection” section. Select a schedule or type in the schedule of your choosing and press “OK”.
Prune Jobs
in the same panel, click on “Add” under the “Prune Jobs” section. Fill-in the panel per this one example:
The settings are explained here: https://pbs.proxmox.com/docs/maintenance.html#retention-settings-example