I have multiple map layouts from a large QGIS project which need editing and updating. The layouts are locked so they can be viewed as printed without updating to the current layers in the main QGIS window. Is there a way to reopen or load the layer from a map layout to view in the main QGIS map canvas window? The same question was poised here Reset canvas match print composer QGIS 3, however as Brian Fisher states the solution of using map themes works for new projects not existing ones where the different map themes have not been set up.
I have reposted the question as there may be new developments since 2 years ago. I am currently using QGIS 3.12.1.