Hi,
Thanks for your answer, but... as already stated: 
Database Type	mysql
Database Version	5.7.32-0ubuntu0.18.04.1
PHP Version	7.3.26-1+ubuntu18.04.1+deb.sury.org+1
Web Server	Apache/2.4.29 (Ubuntu)
Joomla! Version	Joomla! 3.9.24 Stable 
sqlite3 --version: 3.33.0
php -v:
PHP 7.3.26-1+ubuntu18.04.1+deb.sury.org+1 (cli) (built: Jan 13 2021 08:00:44) ( NTS )
mysql: mysql  Ver 14.14 Distrib 5.7.32
MysqlI Support	enabled
Client API library version	mysqlnd 5.0.12-dev - 20150407 - $Id: 7cc7cc96e675f6d72e5cf0f267f48e167c2abb23 $
settings /etc/php/7.3/apache2/php.ini:
Safe Mode	Off
Open basedir	None
Display Errors	Off
Short Open Tags	Off
File Uploads	On
Magic Quotes	Off
Register Globals	Off
Output Buffering	On
Session Save Path	/var/lib/php/sessions
Session Auto Start	0
XML Enabled	Yes
Zlib Enabled	Yes
Native ZIP Enabled	Yes
Disabled Functions	pcntl_alarm,pcntl_fork,pcntl_waitpid,pcntl_wait,pcntl_wifexited,pcntl_wifstopped,pcntl_wifsignaled,pcntl_wifcontinued,pcntl_wexitstatus,pcntl_wtermsig,pcntl_wstopsig,pcntl_signal,pcntl_signal_get_handler,pcntl_signal_dispatch,pcntl_get_last_error,pcntl_strerror,pcntl_sigprocmask,pcntl_sigwaitinfo,pcntl_sigtimedwait,pcntl_exec,pcntl_getpriority,pcntl_setpriority,pcntl_async_signals,
Cache rebuilding, auto-fix and re-index work well. The error shows up on product list only (as in the attachment).
Any ideas?
Thanks