Apple Watch (a series 7) had a white dot top center, and the screen would not scroll up. Couldn't figure it out. Powered off/on to clear it. What was it?

Oh-- apparently a different white dot appears if you use a third party GPS system, and this sometimes causes problems.

Status icons and symbols on Apple Watch - Apple Support

Not sure why you couldn't scroll. My watch has a white dot at top center called the "Now Playing" icon. Apparently it's not there in wathchOS 9