Data source variable with another variable into regexp field

Hi all,
I’m on 9.1.7 grafana version.

I’m trying to achieve a dynamic filter using REGEXP on a data source connection.
I know it’s a little strange but there is a logic on my side… 'cause I got a chained menù that I build with a table on SQLITE.

It’s clear to me the nature of “data source” variable… but at the end of the chain selection on the dashboard I would like to filter dynamically the connection and seems to me that REGEXP field value cannot be a variable, is it true?

Thanks Alen.

Here che data source variable…
$dbinstance is the exact instance that I would like to filter… it comes from a variable… combo menù

Only hard code? No vars below?

I would like implement like this… but seems no hope…

Thanks, Alen

Solved in this way!