To get back to my problem:
The default Ctx bodyfont (CMR) is all right for me, I don't need to change it (but it's possible, if it should simplify something).
If you don't need CMR, than simply don't use. It does not have greek boldmath/upright anyway.
If I understand well, the default Ctx font - CMR - is used for typesetting [bold]math as well. But the problem is that it fails when typesetting bold Greek letters.
Right.
What code - \typescript, \define???font??? - to use?
Just to make the code "$Abc \alpha = {\aSwitchToBoldMath Abc \alpha} = or \aCommandToTypeBoldMath{Abc \alpha}$ work.
Minimal example that uses Tex Gyre Pagella and Heros for serif and sans, and either Cambria, Asana, Neo Euler, or XITS for math (comment in your choice and make sure that context finds the fonts): \starttypescript [myface] \definetypeface [\typescriptone] [rm] [serif] [pagella] [default] \definetypeface [\typescriptone] [ss] [sans] [heros] [default] \definetypeface [\typescriptone] [tt] [mono] [modern] [default] %\definetypeface [\typescriptone] [mm] [math] [cambria][default] %\definetypeface [\typescriptone] [mm] [math] [asana][default] %\definetypeface [\typescriptone] [mm] [math] [euler][default] \definetypeface [\typescriptone] [mm] [math] [xits][default] \stoptypescript \setupbodyfont[myface] \starttext Pagella \par {\ss Heros} \par {\tt Modern Typewriter} \par $Abc \beta = {{\bi Abc} \bf Abc \beta \mathgreekupright \beta}$ \stoptext Note that Neo Euler does not have italics and there are no fallbacks for bold/greek italic. So ${\bi A} \bf \beta$ will be displayed as $A \beta$. Best wishes, Florian