I am attempting to install CiviCRM 5.33.1 on a fresh WordPress 5.6 install. Installation and activation go fine, and I get to the installer page at /wp-admin/options-general.php?page=civicrm-install.
The reason for this new install is that we need to partition CiviCRM to a subdomain on the same shared server as our main site. So I edited the CiviCRM Database setting to use the same DSN as is in our current civicrm.settings.php file, which looks like this:
mysql://[DB user]:[password]]@[server]:[port]/[DB name]
(The CiviCRM database is separate from the main WordPress database on our main site.)
Then I click Apply. The page redirects to /wp-admin/admin.php?page-CiviCRM&q-cificrm&reset=1, which has the title CiviCRM Installed, but then immediately displays the message Sorry, you are not allowed to access this page. That sounds like a permissions problem, but CiviCRM, nor the civicrm folder in wp-content/uploads, isn't installed, contrary to the title of the page.
I can't imagine that it's a problem with the Civi DB DSN, since I copied it directly from the current installation. Or could it be? But how can I figure out what the problem is?