slow_query_log_file has default value if applied in conjunction with max_slowlog_size

I am trying to configure a pxc server with a custom configuration for slow log files, and I need to add the following:

[mysqld]
slow_query_log = ON
slow_query_log_file = /var/lib/mysql/slow
long_query_time = 10
max_slowlog_files = 2
max_slowlog_size = 510000000

so, I created a custom file that will be included in the main configuration and I have shared it when running docker with the following command:

docker run -v $(pwd)/my.cnf.d:/etc/my.cnf.d -e MYSQL_ROOT_PASSWORD=abc --rm -it percona/percona-xtradb-cluster:8.0.36-28.1

when I access container, I see that configuration is not reported correctly inside global vars:

mysql> show global variables like '%slow_query_log_file%'

if I remove max_slowlog_size from custom configuration, Variable_name has the correct value:

This is causing a problem with pmm, since it reads that variable, but it cannot open the file, which is present with the name I specify in configuration:

A similar issue is described here.