After Microsoft's trimming of sharepoint 2010 platform workflows, is it possible to write my own workflow custom activity for platform 2013?

Question

SharePoint

Sharepoint 2019 on premises is running workflows on the sharepoint 2010 platform. Why 2010 - because initially in sharepoint 2019 there was no necessary action to send a letter with an attachment - so a crutch-solution was added in the form of an additional workflow custom activity. Its name is SPD_SendEmailWithAttachment.wsp like this it was set https://www.c-sharpcorner.com/article/steps-to-dep... and in sharepoint designer 2013 the desired action after installation appears only on the sharepoint 2010 platform.

Is it possible to write the most analogue of this solution, but only for the sharepoint 2013 workflow platform?
Since microsoft has cut the sharepoint 2010 workflow platform, our embedded solution no longer works.

Or is there only one way out microsoft power automate? - for us it is not acceptable.

Answer 1

Starting from SP2013, MS made a new platform for Workflow and it is separated by a separate server, and not code-behind as it was before (WF 3.5). Based on this, the approach to development has also changed, now only CSOM / REST actions are deployed to the artifacts folder on the WF4.5 server, and Workflow.XML is added to the SP with a description of these actions. If my memory serves me, that was it.
microsoft power automate - You will have to do a hybrid use case.