Zend certified PHP/Magento developer

Add custom field in shipping address form of Checkout for Magento 2?

Below I have a shipping address form of checkout page and I would like to add another field (P.O. Box) in this form. I tried to look it up every forums and most of the answers were based on overriding.

MagentoCheckoutBlockCheckoutLayoutProcessor.
I checked app/code/company/Checkout/etc/di.xml but wasn’t referencing layoutprocessor.

I am still confused from where this form is getting values from MagentoQuoteApiDataAddressInterface or MagentoCheckoutviewfrontendlayoutcheckout_index_index.xml

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how can I add custom field to this form?