I know that for 2013 and 2016 on premise that there is the capability to adjust a web app setting to allow HTML rending in calculated columnsm via PowerShell:
CustomMarkupInCalculatedFieldDisabled
Links on this:
Handling HTML markup in SharePoint calculated fields
SharePoint Online/2016/2013: HTML Rendering in Calculated Columns
But does anyone know if this web app setting is in SP 2019 on premise?
We will definitely check when we get a SP 2019 farm built but I wanted to see if someone has checked into this already.