SD cards are always going to be slow but looking for the "A2 Application Performance Class" it will give you a tiny boost in "IOPS which is the most important metric for responsiveness.

Source: https://en.wikipedia.org/wiki/SD_card#Application_Performance_Class

...however I don't believe the Pixel 6a has an microSD card slot to begin with.

Source: https://en.wikipedia.org/wiki/Pixel_6a#Reception

The crap shoot of SD card quality along with the headache of having a universal file system if you did remove the SD card has made it go the way of the dodo. Modern phone storage being significantly faster also didn't help things.