@BlueBrenana
Screen mirroring (from Windows) uses a protocol called Miracast which requires that the initial connection between the devices uses 2.4Ghz (for discovery), and then uses either 2.4Ghz or 5Ghz (depending on availability/prior connection).
Firmware/OS/driver updates/configuration along with modem/router/gateway configuration can do limit/impact the Miracast discovery/connectivity process. Microsoft's monthly and bi-annual updates to Windows 10/11 routinely break/limit Miracast connectivity, and you may be running into this (recent bugs/changes limit initial visibility/discovery to 2.4Ghz devices, and after attempted connection to a 2.4Ghz device 5Ghz/other connection devices also appear).
This is not a RokuOS bug/issue, but rather a recent Windows bug/limitation (other OS/device platforms e.g. Android discover 5Ghz connected Miracast receivers e.g RokuOS/FireOS/WebOS without issue).
Make sure your Windows WiFi/Video drivers are updated and Windows is on the latest Windows monthly/bi-annual version, and reboot all devices (Roku TV, modem/router/gateway, Windows PC) - otherwise try forcing network discovery in Windows itself (e.g. disable/re-enable WiFi or Open/Browser Network or Devices & Printers, etc).
