This is an active bug on JetBrains tracker, and the proposed solution above goes against SASS docs and recommendations.
"sass-lang.com/documentation/values/calculations" states that: "You can also use interpolation in a calculation. However, if you do, no operations that involve that interpolation will be simplified or type-checked, so it’s easy to end up with extra verbose or even invalid CSS. Rather than writing calc(10px + #{$var}), just write calc(10px + $var)!"