Gerben Wierda schrieb am 24.04.2020 um 08:48:
With Arial:

\definefontfamily[mainface][rm][Arial]
\setupbodyfont[mainface,10pt]


with Optima:

\definefontfamily[mainface][rm][Optima]
\setupbodyfont[mainface,10pt]

It doesn’t matter if the font statements are before or after \starttext

Then I thought, let’s test some other things. I logged in as another user, and used ConTeXt from TeX Live 2019:

It seems to be that on my system, the standalone installed ConTeXt does not work with Optima, but the TeX Live installed one does.

Can you try this:

\definefontfamily [mainface] [rm] [Optima]
  [it=optimaitalic,
   bf=optimabold,
   bi=optimabolditalic]

Wolfgang