This is provided as-is and no warranty.
This has been tested on Zabbix 4.4, 5.0 and 5.0.2

Workflow

On graceful shutdown/reboot -> Script uses zabbix_sender to send item to Zabbix -> Zabbix triggers based on the received item and an action places the server into "Maintenance Mode" group. On boot -> Startup script uses zabbix_sender to send item to Zabbix -> Zabbix

Steps

1. Create a group called 'Maintenance Mode' Note: Document the groupid which can be found in the URL string when selecting the group within Configuration>Host Groups

2. Create the new item with the key 'maintenance.mode' within the template of your choosing Note: I opted to use Template Module Zabbix Agent

3. Create a trigger with the Problem Expression set to {Template Module Zabbix agent:maintenance.mode.regexp("^Entering Maintenance Mode",1)}=1 and Recovery Expression set to {Template Module Zabbix agent:maintenance.mode.count(15m,"Exiting Maintenance Mode")}>=1 and {Template Module Zabbix agent:maintenance.mode.count(#2, "Entering Maintenance Mode")}=1

4. Copy the files from here to /usr/lib/zabbix/alertscripts/ (or where ever you store your Zabbix scripts, but if you do, you'll need to update the basedir within the script) and update the custom variables section within the .bat file to match your environment. This includes the groupid from step 1

5. Create a new Zabbix action within Configuration>Actions Name: Enter Maintenance Mode

   Conditions: A) Trigger name containers Maintenance Mode B) Trigger name containers Enter Maintenance Mode

   Operations Tab

   Operations:
   Target list: Set this to your Zabbix host Type: Custom script
   Execute On: Zabbix server
   Commands: /usr/lib/zabbix/alertscripts/Enter-MaintenanceMode.bat {HOST.NAME}

   Recovery Operations:
   Operation Type: Remote Command
   Target list: Zabbix host
   Type: Custom Script
   Execute On: Zabbix Server
   Commands: /usr/lib/zabbix/alertscripts/Exit-MaintenanceMode.bat {HOST.NAME}

6. Create a new Group Policy and apply to the OUs you want and set the Computer Configuration > Policies > Windows Settings > Scripts, Shutdown (Enter-MaintenanceMode.ps1) and Startup (Exit-MaintenanceMode.ps1)