Confusion with gauge in yarn pattern

I am planning to knit my first shawl but I am confused about the pattern. It calls for sport weight yarn, but according to ravelry that is 24-26 stitches per inch. However the gauge on the pattern is 20 stitches per inch and uses a size 6 needle. Am I supposed to make a gauge swatch on the larger needles with the sport weigh yarn or is this an error and i’m actually supposed to use a different yarn altogether? I am thinking that lace knitting is different, just wanting to clarify. Thank you!

Lace knitting is different. Patterns often use a lighter weight yarn on larger needles for an open, lacy look.
Start with the yarn weight and needles recommended in the pattern. You can also check on the projects if the pattern is on Ravelry. See what others have used for this pattern.
What is the name of the pattern?

It is Bitteroot by Rosemary Hill.

I’m assuming then that I can’t really do a gauge swatch, I can just try it and see how it goes.

The gauge swatch for the pattern is worked in stockinette so it should be straightforward to determine gauge. It’s a shawl so you won’t have to be precisely on gauge for the project to work.