Chrome 72+ seems to no longer accept --proxy-pac-url

Chrome removed almost all functionality of net-internals for some reason and it sounds like they removed the pac flag that you were using.

chromium docs link to this site that still lists the flag as valid.

https://peter.sh/experiments/chromium-command-line-switches/

Chrome 72-75:

• As suggested in this bug report, you can disable 'Enable Network Service' in chrome://flags to go back to the old behaviour that supports file:// pac files. Starting Chrome from the command-line with --disable-features=NetworkService has the same effect.

Chrome 76:

• It seems that the 'Network Service' option has been removed from chrome://flags (see the code commit).

  You can still run Chrome with --disable-features=NetworkService (ref) (e.g. /Applications/Google\ Chrome.app/Contents/MacOS/Google\ Chrome --disable-features=NetworkService on a Mac), and it seems to read the PAC file ok, though there might be some issues (because lots of related code seems to have been deleted already - see this issue - I guess YMMV, and this won't be a long-term solution.

  As suggested in the bug report, you are probably better either installing a browser plugin that lets you define PAC settings, or use an http(s) PAC file.