The Biden administration has put Cuba on its list of “countries that support terrorism”, along with North Korea, Iran and Syria.
This registration now has a concrete consequence for travellers (see the information shared by the US Department of Homeland Security): "if it turns out that a traveler has visited a country designated as a state sponsor of terrorism, the traveler 'is no longer eligible to participate in the Visa Waiver Program and must apply for a visa to enter the United States'.
Also, if you have visited Cuba since January 12, 2021, you are required to apply for a visa to travel to the United States, whether for tourism or for a business trip. ESTA will no longer be accepted.
What if you already have an approved ESTA?
If you wish to travel to the US again after a recent trip to Cuba, your ESTA will be cancelled by US immigration and you will be denied boarding.
The solution is then to apply for a visa to cover the duration of your stay.
To do this, you will need to go to the US Embassy website, select the Visa tab and apply for your Visa online by yourself.