You are not the first to voice displeasure with the new UI. It's quite a change.
However, there is no way to revert the change without downgrading the OS.
And downgrading the OS is a huge undertaking that includes backing up your files to an external drive, creating a bootable installer (optional but advised), erasing the Mac, reinstalling macOS, setting up a new user account and finally recovering your files back to the startup disk. And there is the potential that any firmware update that may have taken place might require the use of another Mac to restore or revive your computer firmware using Apple Configurator.
Downgrading to an earlier macOS version is not a task to be taken lightly. It's easier and wiser to work through any problems you are experiencing than trying to downgrade macOS.