sorry for the necro but i found a solution for steam users that doesn't need 3rd party software and figured i should share it for anyone else who comes across this thread like me
(quick warning before we begin: if your saves are important to you, back them up first!!)
first, navigate to steam, find stardew valley, find the settings icon,
manage > browse local files
this will show a "Contents" folder. copy this to your clipboard, and make a new folder. put it wherever you prefer (i chose Documents, but it works anywhere) and name it whatever you like, (i chose Stardew.app),
but make sure it ends with a .app extension!!
next, you'll want to right click on the new Stardew.app (or whatever you named the folder/now .app in the past step) and press Show Package Contents.
then, you should paste in the Contents folder from step 2 into this.
almost done! you may want to check if this runs, it did work at this step for me as of writing this, could differ in the future.
finally, you'll want to go back to where you can see the app, and right click on the app and press Get Info.
in that window, you should find a "Scale to fit below built-in camera" toggle. turn that on.
congrats! you should now have a fixed version!
a few things to note before you go off on your merry way:
this may cause issues with your steam saves! i don't know what this could do, but it's not a bad idea to back up your saves first.
stardew seems to do an interesting thing when detached from steam like this - it runs another game, Spacewar, via steam. if you want to know why/what that is, google's free, but it's basically just stardew's way of using steam when it doesn't have a way of knowing if it can properly use steam, as far as i can tell
if you want to still be able to launch the game via steam, follow
this guide and use the .app you should now have
this worked as of posting, on an late 2024 MacBook Pro, with stardew valley v1.6.15 build 24356
hope this helps someone!