How to install DVD format to create DVD?

iDVD was discontinued about 4 years ago and finally, with Catalina, is not longer compatible with the system as it is a 32 bit app and the system requires 64 bit.

There are a number of potential replacements for iDVD at the App Store. Just search for "video DVD".

Two that look promising are Wondershare DVD Creator and DVD Maker Lite - DVD Creator. Both can be run in Demo mode so you can see if it will suit your needs before purchasing.