I did install lsphp74-mysql, of course. But no mysqli with it.
Here's the complete list of the package installed:
lsphp73-apcu/focal,now 5.1.18-1+focal amd64 [installed]
lsphp73-common/focal,now 7.3.28-2+focal all [installed,automatic]
lsphp73-curl/focal,now 7.3.28-2+focal amd64 [installed]...