Sass - TypeError: Cannot read properties of undefined (reading 'indexOf')

My build on the server failed today, suddenly, when doing its Sass thing it's always done for 4 years.

It runs in Docker so the image probably has a later npm than I have locally, since I don't tend to update things that work.

So I updated my local node and npm and replicated the issue.

TypeError: Cannot read properties of undefined (reading 'indexOf')
    at /Users/me/myCode/node_modules/sass/sass.dart.js:116832:12
    at Object.applyHooksTransformer (/Users/me/myCode/node_modules/sass/sass.dart.js:1863:14)
    at Object.initHooks (/Users/me/myCode/node_modules/sass/sass.dart.js:1843:251)
    at Object.initNativeDispatchContinue (/Users/me/myCode/node_modules/sass/sass.dart.js:1809:9)
    at Object.initNativeDispatch (/Users/me/myCode/node_modules/sass/sass.dart.js:1803:9)
    at Object.getNativeInterceptor (/Users/me/myCode/node_modules/sass/sass.dart.js:29308:13)
    at Object.getInterceptor$x (/Users/me/myCode/node_modules/sass/sass.dart.js:29569:16)
    at Object.set$compile$x (/Users/me/myCode/node_modules/sass/sass.dart.js:29636:16)
    at Object.main (/Users/me/myCode/node_modules/sass/sass.dart.js:24401:9)
    at main2 (/Users/me/myCode/node_modules/sass/sass.dart.js:26210:9)

• I've "gone up" through some major versions of both sass and gulp-sass but even latest doesn't work.
• I've cleared the cache and reinstalled these packages.
• I use Sass to build Bootstrap and a single custom.scss file.
• I have not yet checked-out an old commit from Git.
• It last built on Weds 18th Oct and it's now Mon 23rd.
• I've been working far from any of this in C# code.
• I've had only 4 hours sleep and this error showed up on a bad day for me.
• AI is out of ideas.

The failure is spontaneous and unexpected.

My guess is that the Node Docker image was updated this weekend and this has broken Sass somehow.

Updates

• The official Node docker image was updated..... 4 days ago.