I have downloaded Sierra games to run on DosBox on my MacBook Air. I have placed all my GOG downloads into a mac folder and in DosBox I have mounted the c drive to work with that mac folder. The disk mount works fine. When I type "dir" I can see all the .exe files that I've placed into the mac folder. However, when I try to execute any of those .exe files I get the error message "This program cannot be run in Dos mode". Can somebody please help me?

What's the name of the games and the .exe files you're trying to run? I assume you're not attempting to run the GOG installer (e.g. setup_kings_quest_2.0f_(20239).exe) as that'll be a windows file and will require either installing it on a Windows setup or using innoextract to get the files.

Also, If they're newer Sierra games they actually may be Windows programs instead of DOS.

Alternatively if they are DOS games, I know that GOG has replaced some of the Sierra DOSBox builds with builds using ScummVM instead. it may be worth your while to try downloading a ScummVM build that works with your Mac and trying to load a game that way.
https://www.scummvm.org/en/downloads/

If you have a Windows machine with GOG galaxy you can also roll back to the earlier DOSBox builds. Not sure if you can do the same with a Mac, as I don't own one.

Thanks for the reply Crimson. I think I am trying to run a GOG installer. There's a little Windows icon next to the game in the GOG site so that must be the case. I just assumed they would work in a DOS emulator. My bad. I'll try my luck with ScummVM. Also, what is innoextract? Is there a way to extract whatever's in the GOG installer file? Thanks for your help!

Yeah that would be why. A 32/64bit installer trying to run in realmode/16bit environment won't work.

Once you have the files extracted, hopefully dosbox will do the job. Although you MAY decide to use the .conf files offered by the gog game, or it may need tweaking.

Once you get them extracted and moved let us know if you have any issues still. Hopefully you won't have any issues after.

https://constexpr.org/innoextract/#download

https://constexpr.org/innoextract/#download

Yeah, just unpack the games from their installers, and then throw those at the Dosbox flavor of your choosing.

Problem is that often when GOG games are running with ScummVM GOG ommits some files needed for the games to run on DOS Box (because ScummVM does not need them) so not every DOS game here on GOG will run on DOS Box as well.