If your website won't load after updating to BuddyPress 12.1.1 it is likely a conflict with bbPress or another BuddyPress compatible plugin. Install the BP Classic plugin to fix this issue.

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I can't change the site title and description on the homepage?

If you're using the homepage imported from the demo data and have Yoast SEO activated then the site title is being pulled from this homepage. Edit the page, scroll down to the Yoast SEO panel and edit the Site Title field.