I have an Intel Mac running macOS Monterey (12.6.5). If I try to run the offline installer, I get an error about it "can't be opened because Apple cannot check it for malicious software". It is the file stardew_valley_enUS_1_5_6_1988831614_53039.pkg. I get the same error when I try to install the 32 bit package.

Figured it out. It's a security setting on the Mac (not much of a Mac user). You can override it for the installer as found here:

https://support.apple.com/guide/mac-help/apple-cant-check-app-for-malicious-software-mchleab3a043/mac

Basically, right click (or option click) and Open it that way.