I've upgraded to GA4 and kept my UA GA. The upgrade created two new properties: one with a new UA code and another one without. Of course the new property with the new UA doesn't get any traffic since I didn't add it to the site.
I managed to connect the original GA account to the GA4 property that doesn't have a UA code, but even if it says "connected" and the GA4 shows some traffic data, the data is not the same between the GA and the GA4. For example, real-time report in GA4 is always in 0 even if I have traffic in the real-time report in GA.
Does anybody know if I should set up the UA code of the GA4 new property in the site anyway? Can I delete the UA GA4 property? (!) Is it the reason why the data that the GA4 property is not the same as in the GA original account?