Hey--I run both platforms and I think you can't go wrong either way for security. By far the greatest vector for malware/'hacking' will be through vectors like browser extensions, clicking on phishing links in emails/texts, user error stuff like that. Both platforms are well hardened against that type of malware, but if your concern escalates above that into directly being targeted by the state or another similar scale adversary then I'd 100% go with GOS.
As far as privacy goes, GOS wins imo. iOS has a reputation for good privacy but I've noticed from my controlD logs that my pixel running GOS has no background/idle network chatter and sends out no telemetry, whereas the most blocked domains are all iOS telemetry from my iphones. GOS also does a better job of letting you fine tune app permissions with deeper control than iOS imo, such as with storage scopes.
I will say the downside of running a multiplatform setup is losing out on the ecosystem of convenience, especially for your situation coming from an all-apple setup. If you don't feel super inclined to stick with icloud, safari, keychain, etc there's many cross platform apps to replace those like ente, brave, other password managers, etc that you can run on macos and GOS.
Also imo the best way to harden your personal security goes beyond what OS you use--freezing/locking credit reports, using email aliases for everything, 2FA on all accounts, and removing your info from data brokers is far more impactful imo.