MacOS – Compress a folder into multiple zip files

In winzip: Add the files to the zip either by starting up winzip and adding or drag and drop into winzip or right click on the files and winzip 'add to zip...'

Then in winzip:

Actions - Split at the bottom of 'part size' pick 'other size' then put 20 and select mb

Done!

WinZip (or any modern compressing software) can't know before compressing what will be the size of compressed data. On top of that, the size of a compressed file would change (by a tiny bit) depending of the nearby files data. So if that's not theoretically impossible, WinZip is not able to do this nor any data compression software I know of, as it would involve compressing the data many times to get the closer matches. Your best hope is to manually select groups of files and compress them to get ~50MB files. And when I write "manually", you may want to try writing a script doing the work for you. But I guess 50MB is not a hard limit, and you could just use the approximation method by hand.