Frickler

...would require GROUP BY, and then problems arrive with "AA" and "BB" not being grouped.

The User Table is named MON$ATTACHMENTS See https://firebirdsql.org/file/documentation/chunk/en/refdocs/fblangref30/fblangref30-appx05-montables.html#fblangref-appx05-monattach

FireDAC doesn't support Paradox at all. You have to port to another Database, e.g. Firebird. But beware, no more SetRange and Filter, but SQL only.

I don't think so. I think InterBase is designed to be very slim and fast. For example, for everything except the most essential internal functions you have to use UDFs. Furthermore, it looks to me that the main use case is still embedded SQL like in ye olden times of InterBase on UNIX.

With Update 2, Interbase 2020 has now CTEs.

Don't add "Port" and "Protocol" if using embedded.

Interbase has virtually no internal functions. Not even in the newest versions. All has to be done in UDFs. The Firebird developers on the other hand had changed that from the beginning.

Full support including the new 128 Bit types, timestamp with timezone and the new batch API for INSERT/UPDATE? I ask because UniDAC/IBDAC only supports a subset at this time.

Using SQL, it's slow. But Absolute Database isn't made for SQL, but for good ol' ISAM: IndexName, SetRange, Locate, Filter, you name it. There (and in single user mode) it is really fast. And you not only don't need any DLLs to access it, you can even embed the database into the EXE (for read only databases such as catalogues).

But interposers did.

It's possible that Interbase supports only "simple case", that is case foo when 1 then 'one' when 2 then 'two' else 'many' end

What if you remove the parentheses around the case statement?

Is it possible to do manipulations like "multiply all 'Left' properties by 2" using this DFM Editor?

Pascal example: https://github.com/Arcantar/FirebirdSQL_Sample

Could you please provide the source code of your little demo?