"Not Found Error" on Admin --> Appearance Page

First post, so please pardon me if I missed a solution to this issue prior to posting here.

I’m able to navigate to any of the pages linked to by the Admin portal, except for the “Appearance” page (via the tab at the top navbar). When I try to navigate there, I get the error attached below.

I’m developing locally prior to rolling out publicly using Ubuntu 20.04, Apache 2.4.41, MySQL 8.0.25, PHP 7.4.3. I’ve changed all “AllowOverride” fields to “All” in the apache2.conf file. Not sure what could be going wrong with the “Appearances” since everything seems to be working fine. Many thanks for your help!

Edit for clarity: I’m running Omeka Classic 2.8

Everything else works on both sides, just not this specific page?

Sorry for my delay! Yes, everything else is working except for this one page. I’m attempting to access it from the Admin Dashboard “Appearance” button in the top navbar. The url displayed when the button is hovered over is “localhost:8000/admin/appearance”, and it automatically reroutes to “localhost:8000/admin/themes/browse”, which is where I get the 404 error. Not sure if that’s relevant or not. Any help/insight is much appreciated!-Robby