Unfortunately clustered storage is just a hard problem, and there is a lack of good implementations. OCFS2 and GFS2 exist, but IIRC there are challenges for using them for VM storage, especially for snapshots. Proxmox 9 added a new feature to use multiple QCOW2 files as a volume chain, which may improve this, but for now that's only used for LVM. (Making Proxmox 9 much more viable on a shared iSCSI/FC LUN).
If your requirements are flexible Proxmox does have one nice alternative though - local ZFS + scheduled replication. This feature performs ZFS snapshots + ZFS send every few minutes, giving you snapshots on your other nodes. This snapshot can be used for manual HA, auto HA, and even for fast live migration. Not great for databases, but a decent alternative for homelab and small business.
If your requirements are flexible Proxmox does have one nice alternative though - local ZFS + scheduled replication. This feature performs ZFS snapshots + ZFS send every few minutes, giving you snapshots on your other nodes. This snapshot can be used for manual HA, auto HA, and even for fast live migration. Not great for databases, but a decent alternative for homelab and small business.