Sorry to inform you that if you are not getting option in you sub-domain then this issue is not related to the theme.
Cause the option you get on theme doesn’t change with the main domain or sub-domain.
This issue might have resulted due to other issue rather than the theme itself.
If you have installed any third party plugin then try disabling them one by one to see if any plugin issue exists.
If the issue doesn’t resolve then try accessing the static front page option from Admin Panel / Appearance / Customize / Static Front Page.
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