We just went live on NetSuite last month. Now, our implementation partner is wanting to charge us to convert JSass to Dart Sass. I found the announcement from July of last year regarding the end of support for JSass. My question is, could our website have used Dart Sass prior to the release of 2024.1? Our implementation project kicked off in April of last year, was Dart Sass available in SCA at that time?

No it was not available last year. Fixing those issues is easy. I did it for my theme.

if you are using SC Standard and using the NetSuite provided theme as-is and have extensions that are JavaScript focus (I mean not styling/theme focus), you might not need to take any further actions. I would advise understanding the customization(s) installed and/or built for your SuiteCommerce (if any), can avoid you getting ripped off. My 2cents. Have a great weekend!