We read a lot of advice on The Joomla! Forum™ and elsewhere about the end of support for PHP 7.4 set to occur on 28 November this year.
Have you ever heard the story of the ancient city Troy? It had massive walls, keeping attackers outside and the city safe. However, the greek army, attacking the city, had a genius idea: they pretended to stop their attack and travel back home, while leaving a gift for the people of Troy: a huge wooden horse. The people of Troy were thankful for that gift and pulled the horse inside the city's walls - not knowing that greek soldiers have hidden themselves in the horse, crawling out at night, opening the doors for the rest of their army and thereby dooming the city.
Joomla 4's now available, but if you're thinking about upgrading from Joomla 3.9, here's some important things to keep in mind before you click the Update button.