This is how to migrate UA Annotations into GA4 in 3 min.
The first step is to copy your annotations from your Google Analytics (UA) account:
1- Open Google Analytics UA property
2- Go to Admin on the left side menu
3- Click "Annotations"
4- Copy the list (select/mark it and copy ctrl-c)
Now is the time to upload and display in GA4
5- Log into your Crystal Ball account.
6- In the annotations list page, Tap “CSV Upload” to proceed.
7: Download the sample CSV excel sheet to copy your annotation list into it.
8- Paste the annotations from UA (from step 4) into the sample CSV file
9- Choose your GA property linked to this list of annotations and click "Upload and Preview"
10- Map the columns
11- If there is any error, fix the marked fields and continue until everything is good to go.
12- Click on “Submit” and you have successfully uploaded your list of annotations
13- If you still don't have the Crystal Ball Extension installed, download the Chrome Extension and login
14- Go to your GA4 account and click on the dots over the GA4 charts
Now, you have successfully transferred your annotation data from UA into your GA4 property.