Similar issue here on a 13" MacBookRetina late 2013 connected to an external Iiyama display.
Both display turn black randomly and stay black (external display shows "no input") until I close and reopen the MacBook which I normally had used in clamshell model until this error occurred.
No True Tone on this device but automatic nightshift (turned off now for testing).
No errors shown in console.app but a report which might be the same time as the last incident:
displaypolicyd.0:2:0.log:
2021-01-05 11:48:25.896107+0100: NOTICE: accepted No_Media_Mode enter, Tue Jan 5 11:48:25 2021
2021-01-05 11:49:02.552431+0100: NOTICE: accepted No_Media_Mode exit, Tue Jan 5 11:49:02 2021
2021-01-05 11:49:16.114755+0100: NOTICE: doChange: addr 1.0 [7]
2021-01-05 11:49:16.116346+0100: NOTICE: doChange: addr 2.0 [7]
2021-01-05 11:49:16.126679+0100: NOTICE: doChange: addr 3.0 [7]
2021-01-05 11:49:16.180639+0100: NOTICE: Port non-scanned FB[ 2 ] link is good ...
2021-01-05 11:49:16.446031+0100: NOTICE: Populated addr 3.0 26cd:6637 UUID d6040000 order 0:0 tx 2:2 dsp 1 WL 0 MS 0 edid 256 undef 0 DSC 0
2021-01-05 11:49:16.446139+0100: NOTICE: Device addr 3.0 is same ...
Any help on this would be highly appreciated...
Never had this problem before updating and using Big Sur.
Edit: found another report:
ims-2021-01-05-11-48-20.log
11:48:20.110 INFO [date]: Tue Jan 5 11:48:20 2021
11:48:20.110 DEBUG [awd.location]: E911LocationAwd Constructor
11:48:20.111 DEBUG [bambi.call]: EmergencyCallhandler: resetting conditions
11:48:20.111 DEBUG [power]: SleepWakeMonitor started
11:48:20.112 DEBUG [util]: Adding observer 0x7fbaedf20b50 for NSSystemClockDidChangeNotification
11:48:20.112 SPAM [sip.lock]: SimpleNetworkManager: acquired lock [BambiClient] (count=1)
11:48:20.112 DEBUG [bambi]: =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
11:48:20.112 DEBUG [bambi]: = Welcome to Bambi! =
11:48:20.112 DEBUG [bambi]: =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
11:48:20.113 DEBUG [prefs]: Key found in prefs file: ImsLoggingEnabled with value: 1
11:48:35.079 DEBUG [ims.irat]: Register IMS-iRat Client
12:06:34.875 DEBUG [ims.irat]: Register IMS-iRat Client
12:14:28.402 DEBUG [ims.irat]: Register IMS-iRat Client
12:14:55.564 DEBUG [ims.irat]: Register IMS-iRat Client