Easy to switch themes/modules from 2.3.6 backup to 1.9.x?

[f1-outsourcing]

Is it easy to convert 2.3.6 themes/modules to magento-lts?

I know this is a broad subject, but what is the general experience porting such things back?

eg. using the api in 2.3.6 like this

<?xml version="1.0" ?>
<routes xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:module:Magento_Webapi:etc/webapi.xsd">
	<route method="GET" url="/V1/orderprocessing/payment">
		<service class="F1outsourcing\WebhookOrderProcessing\Api\ManagementInterface" method="getGet"/>
		<resources>
			<resource ref="anonymous"/>
		</resources>
	</route>
	<route method="POST" url="/V1/orderprocessing/payment">
		<service class="F1outsourcing\WebhookOrderProcessing\Api\ManagementInterface" method="getPost"/>
		<resources>
			<resource ref="anonymous"/>
		</resources>
	</route>
</routes>

[Flyingmana]

Porting things back from Magento2 is currently a big effort, especially if its about themes/templates, as the whole architecture did change in Magento 2.

Regarding API there would be an option to add a compatibility layer, but thats likely a lot of work to make part of our core.