How often do you apply proxmox updates?

Patches are sent to the pve-devel mailing list. They get applied as soon as possible to git. How long it takes the packages to then arrive in public repositories is not fixed. For example, if something has been broken by accident, it is likely to be published faster.

You can get commiter date & subject by git log --format="%cD %s". For pve-manager (one of the more important repositories) you get:

Code:
Sat, 6 Feb 2021 15:16:22 +0100    fixes #3066: resourcestore: add vm hostcpu/hostmem fields
Sat, 6 Feb 2021 14:28:39 +0100    ceph: add get api call for single pool
Sat, 6 Feb 2021 14:25:53 +0100    ceph: add titles to ceph_pool_common_options
Sat, 6 Feb 2021 14:24:30 +0100    ceph: setpool, use parameter extraction instead
Sat, 6 Feb 2021 14:17:53 +0100    api: ceph: subclass pools
Sat, 6 Feb 2021 14:04:40 +0100    api: Ceph: add reminder to remove 'disks' call
Wed, 3 Feb 2021 08:36:59 +0100    ui: qemu/HardwareView: check EFI Disk button permissions
Wed, 3 Feb 2021 08:36:59 +0100    ui: qemu/HardwareView: change heuristic perms to const
(...)

And
Code:
apt changelog pve-manager
might be interesting as well.