Is the ATK test required for entry to Thailand in April 2022?

In Thailand yes only until the 1st May

For what and where?

If you arrive in April you will take a PCR test when you arrive and wait for the results in your hotel. You should also receive an ATK which you will take on Day 5 and report the results through the Morchana app. Both tests are required and you can be fined up to 20,000₿ when you leave Thailand if you did not take and report your day 5 test, but it's very rare.