I had a few fun and games installing the older driver, and from memory it went like this.
Firstly remove the newer driver:
# cd /Library/Extensions
# rm -rf FTDIUSBSerialDriver.kext

...and reboot. Verify after reboot that NO FTDI driver is installed with SystemReport -> Extensions.

Now install the older (unsupported) driver, version 2.3, using the procedure described here after installation, from direct.ilink.de/en/usb.html and screenshotted below. This procedure is for a different driver but the instructions are still the same. Note that you do not get this option with the newer FTDI driver, it just fails to load silently

...and reboot when installed. And using SystemReport -> Extensions, you should see the loaded driver, or that worked for me anyway, on Catalina 10.15.3 on my iMac and my MacBook Pro


FTDIUSBSerialDriver:
Version: 2.3
Last Modified: 02/03/2015, 15:37
Bundle ID: com.FTDI.driver.FTDIUSBSerialDriver
Notarised: Yes
Loaded: Yes
Obtained from: Identified Developer
Kind: Intel
Architectures: x86_64
64-Bit (Intel): Yes
Location: /Library/Extensions/FTDIUSBSerialDriver.kext
Kext Version: 2.3
Load Address: 18446743521889628000
Loadable: Yes
Dependencies: Satisfied
Signed by: Developer ID Application: Future Technology Devices International Limited (658CPPCMJJ), Developer ID Certification Authority, Apple Root CA

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