If you build your app on Monterey, you don't need any helpers or tricks. An app compiled on macOS Sonoma or earlier (eg Monterey) supports QuickLook correctly on any macOS from High Sierra to Sequoia (inclusive). The problem is in building an app on Sequoia and Xcode 16 to work with QL on macOS BigSur and earlier.

After adding quicklookui as optional, the problem is solved partialy: the app starts under older macOS but the QuickLook functionality is not available - even after linking quicklook in addition to quicklookui

Downloading Xcode from Developer account is wasting of time. It's exactly the same build level as the version from the App Store (13C90). Knowing the speed of fixing bugs with Xcode, better downgrade to the version 13.1