Toast Titanium won't burn 4.4 GB disc image to DVD - WHY?

I just recently switched to a newer iMac and paid to run Toast Titanium 20 on Sequoia 15.4.1

Previously I could burn a DVD from a disc image (.iso or .toast) using Toast Titamium 11 without a problem,

Now when I load up any of the disc images saved previously it either fails to burn the DVD with various error messages or even start the process because Toast tells me the file 4.41 GB is 'too large' to fit on a 4.7 DVD !

I tried the single disc image and the cross platform options but it failed with the former and wouldn't start with the latter. The compress to fit option in Burn DVD doesn't help because I need to use Copy for converting the disc image to DVD.

I am using the same media as I always have.

Baffling.

Help!