MySQL encoding problems in Docker

Question

• There is docker container with mysql:5.7.36
• There is docker container with php:8.1.9-fpm
• PHP works with MySQL via PDO-driver (Laravel in php container to be more precise)
• There are two hosts: Ubuntu 20.04 and Debian 10. Both have identical copies of these containers.
• Thers is a SQL-dump that executed on mysql on both hosts.
• Charset in CREATE TABLE's is utf8mb4
• Dababase contain texts in Dutch.
• SELECT in PHP code returns correct texts on Ubuntu host, but broken on Debian ("officiële" instead "officiële", for example)
• In mysql-console result is correct on both hosts
• I have tried SET NAMES utf8, SET NAMES utf8mb4, SET NAMES utf8mb4_general_ci, SET NAMES utf8mb4_unicode_ci and no SET NAMES after connection. It doesn't work.
• mysql -h --verbose returns identical results on both hosts
• SHOW VARIABLES from PHP-connection returns also identical results (except hostname)

What else can be checked?