Newer computers support modern standby and the OS (Windows 10, 11, etc.) will enable it when present and supported in computer firmware. The Power management under network adapters is no longer present when your computer is running in modern standby mode (S0 sleep mode*)* because it no longer applies in that mode for those particular devices. You would have to force your OS to run in legacy standby (S3 sleep mode) for the option to reappear for network adapters. Your current network adapter and its drivers and/or firmware may simply have issues with modern standby or it may even be defective. This leaves two solutions. Either obtain a replacement adapter/driver that functions properly in modern standby or force your computer to function in legacy standby mode. Upon restart the power management tab for network devices will reappear.
Execute the following reg commands from an elevated command prompt to modify OS behavior:
Disable Modern Standby (Forcing legacy standby S3)
reg add HKLM\System\CurrentControlSet\Control\Power /v PlatformAoAcOverride /t REG_DWORD /d 0
Revert to Modern Standby (S0 Low Power idle)
reg delete "HKLM\System\CurrentControlSet\Control\Power" /v PlatformAoAcOverride /f
For more information on this topic: Modern Standby vs S3