within our SharePoint 2016 on prem environment we connected local SQL servers via BCS then added a search content source for that and used custom search templates to visualize this SQL data in SharePoint search.
As it is possible to use BCS with Azure SQL in SPO as well, I see a way how to show SQL based data in modern SharePoint sites.
As the data I want to use in on prem and I have no chance of getting them to Azure I wonder if it was possible to connect External Content Type in SharePoint Online to local SQL over the "On Premises Data Gateway" that Power Bi and Power Apps use easily.
Or do you see another way of getting lots of local SQL data to be shown in modern SharePoint Search?
Would be pleased to hear your opinion about how to do that or if it was possible.