It is great that you want to spend your holidays in Ireland!
Regarding the restrictions, you are right. Ireland's travel advice will be reviewed on July 20th. The quarantine on the island will be reviewed that day as well, so it may be lifted for some countries but it is not clear if it will be lifted for the UK. The best we can do is to wait for the list of 'green countries' to be released on that day.
I hope by September the situation will be better.