I’ve browsed the Discord and it seems a number of people have had this issue.
Despite having connected the Wii remotes to Bluetooth successfully (they’re visible in Windows Bluetooth as “Connected”), Driver4VR fails to see the controllers and they continue flashing forever.
Apparently a workaround is to use the Dolphin emulation software to allow Driver4VR to “see” the Wii remotes. However this is hit-and-miss as well as obviously not intended.
Supposedly this issue is only encountered when pairing Wii remotes that weren’t paired in previous versions of the software. New model Wii remotes don’t work at all. My Wii remotes are first generation and I’m having the same issue regardless.