Why don't reports show today's transactions (conversions)?
Each event should be marked as conversion appears in the reports with a delay due to the conversion model.
Conversions are now called key events. Check out the details on key events here. In addition, you can learn more about modeled key events in Google Analytics 4.
As stated by Google, “Marking an event as a conversion affects reports from the time of creation. It does not change historic data. When you mark an event as a conversion, allow up to 24 hours for it to show up in standard reports. Realtime reports update sooner, at some time after a user triggers a conversion event.”