Wordpress Site Navigation & Layout Repair -- 2

My WordPress site is experiencing design/layout issues. The site has been copied to a test bed to update the PHP and theme. The test bed site PHP has been updated from 7.4 to 8.2, and the theme, Startit, was updated from 1.4 to 5.0. The site appears stable, but elements of the site have stopped working, including (1) layout and wrapping of header icons when page size changes, including mobile, (2) right-hand sticky buttons have been lost, and (3) our "Reserve number" page, which uses Ninja Forms and a custom API, has stopped working. We would also want plugins reviewed, removing any unnecessary, ensuring no errors are left in logs when work is completed.
I need a skilled WordPress developer to diagnose and resolve these issues so my site is once again working and stable. Please provide a bid if you have experience with WordPress site repairs, specifically with Ninja Forms and API's. All changes, repairs and updates should work when the work has been carried out and we will migrate the test bed back to the live domain and require additional work to complete within the project.