How many layouts can be created in a single project?

[AleydaMcDonald]

ArcGis Pro 3.1.4.

[DanPatterson]

There is no specified limit.  For more information on Layouts, you can explore the help topics beginning here...

Layouts in ArcGIS Pro—ArcGIS Pro | Documentation

[Robert_LeClair]

I'm sure there's a functional limit to the number of layouts in an *.aprx but the standard messaging is unlimited number of layouts.