There appears to be an issue when using Experience Builder's sidebar feature. Map widgets such as the "+", "-" and the home button above the sidebar do not work when the sidebar is open, however, once the sidebar is collapsed, they operate as intended. The same issue occurs when the sidebar is located on the right side or bottom of the application. https://experience.arcgis.com/experience/e31d78321154468389cea9aecd7edecf/?draft=true
Sidebar open and no map widgets above the sidebar work.
Sidebar collapsed and map widgets above the sidebar work.
It looks like you have encountered a variant of what I call the sidebar problem.
Even though you have designed your sidebar so that it doesn't cover up the whole side of the screen, the box it expands into still covers the whole side of the screen blocking any interaction with the widgets below.
(Also, try panning your map so that some of the points are where the sidebar would be. I bet you won't be able to trigger a popup in that area.)