There are 9 days left until 32-bit macOS games on Steam will be unsupported. Here is an announcement from the Steamworks doc page:
Speaking of 64-bit, here is an interesting article on a dev's experience with his game on macOS.
Starting October 14th, 2019 Steam will require all new macOS Applications to be 64-bit and notarized by Apple. If your Mac application already supports 64-bit, please login to Steamworks and select the "macOS -> 64 Bit Binaries Included" checkbox in the "Supported Operating Systems" section for your application. This will ensure that your macOS app will appear as compatible for users who are running Steam on macOS 10.15.
Speaking of 64-bit, here is an interesting article on a dev's experience with his game on macOS.

Sorry macOS users, but Apple has gone too far for some of us devs
Why I've had to decide to not officially support Macs for Cogmind or my other software.
www.gridsagegames.com