Creating expression that combines data from multiple data sources

Grafana version 9.1.6

I have two separate data sources, both of which are Influx databases, configured to use Flux. Let’s call them DataA and DataB, which are time series of boolean data returned by QueryA and QueryB, respectively. These two queries are produced in a panel by selecting ‘Mixed’ as the ‘Data source’.

I now wish to return a time series which is the result of DataA AND DataB. This is straightforward when the queries are from the same data source - I can use an expression. However, with a ‘Mixed’ data source it seems I am forced to pick a data source for my expression, and upon doing so it is changed into a query. If I don’t and leave the drop down as ‘Expression’ I get a ‘Query error 500’.

How can I achieve this please?