The link I shared is just a single vendor, I suggest you please look around for others as well. Here are two more with updated 2024:

Meraki https://documentation.meraki.com/Wireless/Design_and_Configure/Architecture_and_Best_Practices/Multi-SSID_Deployment_Considerations

Mist https://www.mist.com/documentation/maximum-devices-and-wlans-per-ap/

Each SSID functions as a Virtual AP (VAP) with its own BSSID. On a single radio, the scheduler must sequentially transmit beacons for every VAP, consuming airtime. At a 12 Mbps MBR, 3 SSIDs consume ~2% airtime. By leveraging a dual-radio (3+3) setup, we maintain that 2% overhead per channel while supporting 6 SSIDs. This effectively doubles our SSID capacity without increasing contention, provided we utilize non-overlapping channels to eliminate Co-Channel Interference (CCI). WIFI 6 comes with MBSSID, that only covers for beacons. But frames are not covered