MacBook Air M4 and MacBook Pro M1 external monitor wakes in sleep

I’m using a MacBook Air M4 and a MacBook Pro M1 Pro running macOS with a Samsung LS27A800U 27” 4K IPS monitor connected by USB-C using DP-Alt Mode with power delivery. When the Mac enters sleep, the monitor briefly turns on, then goes into standby, then wakes again, looping continuously. Each handshake causes the Mac to play the charging-connect sound. I want the monitor to remain in standby/off until I manually wake the Mac, without disconnecting anything.

I’ve tested every relevant monitor OSD setting including disabling automatic source switching, eco timers, and adaptive brightness controls, and I updated the monitor’s firmware from version 1002 to 1007.1 using the supported USB flash method, but the behaviour did not improve. On the Mac side I disabled Proximity Wake and Wake on LAN with Terminal, and I’ve already turned off Wake for network access, Bluetooth wake, and analytics sharing while keeping tcpkeepalive enabled to preserve Find My functionality. The issue remains only when USB-C carries both video and power during sleep, and I’m looking for a low-impact, supported macOS-side sleep policy override or workaround that stops the system from waking the external display without affecting Find My.