OK, looks like i somehow fixed it myself. what i did (just for reference) :
1. there was a problem with my reverse proxy config, looks like it changed with this version.
old version that works till version 1.4:
ProxyPass / http://<LAN IP>:8088/guacamole/ flushpackets=on
new version, works with version 1.5:
ProxyPass / http://<LAN IP>:8088/ flushpackets=on
2. after upgrading to 1.5 this time mysql started just fine, but there was an errors in mysql.log:
2023-05-05 20:45:18 0 [ERROR] Incorrect definition of table mysql.event: expected column 'definer' at position 3 to have type varchar(, found type char(141).
2023-05-05 20:45:18 0 [ERROR] Incorrect definition of table mysql.event: expected column 'sql_mode' at position 14 to have type set('REAL_AS_FLOAT','PIPES_AS_CONCAT','ANSI_QUOTES','IGNORE_SPACE','IGNORE_BAD
2023-05-05 20:45:18 0 [ERROR] mysqld: Event Scheduler: An error occurred when initializing system tables. Disabling the Event Scheduler.
after quick googling i found that it should be fixed with this command inside docker container:
mariadb-upgrade -u root -p
BUT, this command was not found in docker image used, so i installed it myself with command (again, inside docker container) :
apk add mariadb-server-utils
and executed mariadb-upgrade command above and it fixed my mysql installation.
looks like all is working just fine now, quick docker restart shows no more errors in mysql.log.