Galaxy Flip
Boot Samsung Galaxy Z Flip 4 into Recovery using ADB command
First of all, make sure you have installed Samsung Galaxy Z Flip 4 USB Driver and ADB and Fastboot Drivers on your Windows PC. Enable "USB Debugging" on your phone from Developer Options. If Developer Options is missing; go to Settings > About Phone and tap on Build Number for about 7-10 times. Connect your device to PC and open Command Prompt (CMD). Enter the below command to boot Samsung Galaxy Z Flip 4 into Recovery Mode.
adb reboot recovery