I'm glad if you found something new for you. As for ga function, you are right. I should have missed that moment. I rechecked GA docs and indeed, analytics.js redefines ga function. That makes me wonder how could I see my custom metric when I tested my proxy solution. I should give it a second look. Anyway that's not a prod-ready solution so no damage done :)

Did you mind to use GTM or custom GA4 solution to completely replace a default GA analytics?