Define "pretty big". Proxmox officially supports up to 32 nodes in a cluster and the Proxmox folks themselves have "seen clusters of around ~24 nodes in production" (as of 2025) and for "bigger clusters than that, fine-tuning might be necessary":
* https://forum.proxmox.com/threads/proxmox-with-48-nodes.1746...
There are folks talking about running things in the high-40s and low-50s, but that's not officially support. If you have beefy hardware you can fit a lot of VMs on a single hypervisor (I've always found running out of RAM is often the limit).
A single vSphere cluster can have up to 96 nodes (without vSAN), and vCentre can handle multiple clusters (2500 total hosts; 40k VMs). Proxmox recently released Cluster Manager, which helps with feature parity.
I'm a happy user of Proxmox for a number of years (and helped ran OpenStack before that), but I think for large(r) scale deployments (and even smaller ones) there's a good reason which VMware was so popular. (How many folks are actually at that (large(r)) scale is a different question.)
(Also: XCP-ng doesn't seem to get much press. Haven't used it myself though.)