Update Win x64 from 1909 -> 2004 killed Realtek line-in audio at both rear blue and front pink jacks (tested independently). Jack plug-in actions auto-detected normally. Sound app "Listen to this device" enabled. Software level meters show no signal, despite actual normal line-in-level signal. Optical audio out is unaffected - still plays system sounds. Realtek driver update to 6.0.8967.1 has no effect.
This week DisplayPort video began to drop out intermittently while idling. Switching to HDMI fixed the video dropouts, and line-in audio returned!!