Answer

1. If the monitor are connected to NVIDIA or AMD graphics card, with "G-Sync/G-Sync Compatible" being enabled in NVIDIA Control Panel (Enabled both "Enabled G-SYNC, G-SYNC Compatible" and "Enable settings for the selected display model" options) or with "FreeSync Premium" or "Adaptive-Sync Compatible" being enabled in AMD Software. The options would be greyed out.
2. If the monitor are connected to PS5 or Xbox, when "VRR" option being set to "Automatic" in PS5 or "Allow variable refresh rate" option being set to enabled in Xbox, the options would be greyed out.