This python script will make iTerm with your macOS theme. (Requires a Profile called Light and Dark)

auto_theme.py

#!/usr/bin/env python3

import asyncio
import iterm2

async def main(connection):
    app = await iterm2.async_get_app(connection)

    effectiveTheme = await app.async_get_variable("effectiveTheme")
    
    parts = effectiveTheme.split(" ")
    if "dark" in parts:
        preset = 'Dark'
    else:
        preset = 'Light'

    profiles=await iterm2.PartialProfile.async_query(connection)
    for partial in profiles:
        full = await partial.async_get_full_profile()
        if partial.name == preset:
            await partial.async_make_default()
            for window in app.terminal_windows:
                for tab in window.tabs:
                    for session in tab.sessions:
                        await session.async_set_profile(full)

    async with iterm2.VariableMonitor(connection, iterm2.VariableScopes.APP, "effectiveTheme", None) as mon:
        while True:
            theme = await mon.async_get()

            parts = theme.split(" ")
            if "dark" in parts:
                preset = 'Dark'
            else:
                preset = 'Light'

            app = await iterm2.async_get_app(connection)
            profiles=await iterm2.PartialProfile.async_query(connection)
            for partial in profiles:
                full = await partial.async_get_full_profile()
                if partial.name == preset:
                    await partial.async_make_default()
                    for window in app.terminal_windows:
                        for tab in window.tabs:
                            for session in tab.sessions:
                                await session.async_set_profile(full)
                    
iterm2.run_forever(main)