I’m running a plain Astra theme, using an Elementor header template and a standard WordPress sidebar. I’ve had to activate the “Enable FSE theme support” setting in the “bbp style pack” plugin, otherwise any searches return a 500 error.
Everything looks fine viewing the forum root page if you’re not logged in, but if you are, the page loses the header, footer, and sidebar (see the screenshots below).
I know the warning on the Theme Support setting says “much of the functionality of WordPress eg Sidebars, conditional logic etc. is not easily achieved.”, but I would think if that were the case I wouldn’t see the two versions.