Mike Okuda mentioned on twitter that helvetica ultra compressed was used, and sometimes letraset compacta, and sometimes other fonts if needed. Swiss 911 ultra compressed is a good stand-in, because it’s one of many fonts made by another company explicitly to imitate more mainstream fonts. However, Neue Helvetica is probably the best font to get currently, since it was created with modern digital font use in mind.
It’s also worth noting that Tungsten, which looks very much like Helvetica, was used as the LCARS font in Picard (https://twitter.com/HoeflerCo/status/1220748796101120001). It’s even more expensive if you buy every style, but I think the Tungsten family looks pretty good, and is another font created for modern digital typography. I also personally think that that Tungsten is probably the best LCARS font, since it comes in so many different styles that are generally similar, whereas the Helvetica family isn’t quite as unified/“LCARS-looking” once you move away from the ultra-compressed styles.