Hi Ch33n0
To get back to Safari 14.0, I had to reinstall mojave, that returned me to Safari 12.1.2. I then added the macOS supplemental update, and security updates - making sure to not update Safari to 14.0.1
To start the reinstall process Apple provide a macOS installer available from
macOS Mojave 10.14
This will give you mojave 1.14.6 and Safari 12.1.2
If you then goto System Preferences, Software Update. Underneath the Catalina update notification, there will be a sentence "Other updates are available", click on the more info link, and then uncheck the Safari 14.0.1 - you can install/update the rest.
Its a slow process on my old iMac late 2012, but it is straightforward.
Just remember to keep unchecking the Safari 14.0.1 install, in the software update pane (in my case underneath the catalina update blurb) after the mojave reinstall.
Safari 14.0 comes bundled in the macOS supplementary update - and that's where I've left it for now.
The 2 security updates are fine to install.
good luck