Calendar (plugin) not present/working with Docker installation?

Hello.
I’m running Kanboard in Docker on Synology NAS .
I’ve changed php file to activate plugins, however calendar plugin is not listed in directory. (btw Other plugins I installed work just fine)
Also… I tried to use Calendar iCal feed to see tasks using 3rd party calendars… It seems to only export current events/tasks but does not update anything… (perhaps cos calendar plugin is missing?)

My data and plugin folder are within docker so not sure yet how to copy calendar plugin for manual installation… I thought to first ask if there is anything else I need to know (reason why calendar plugin isn’t listed)

Thank you

Configuration
Application version: v1.2.13
PHP version: 7.3.11
PHP SAPI: fpm-fcgi
HTTP Client: cURL
OS version: Linux 4.4.59+
Database driver: sqlite
Database version: 3.28.0
Browser: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/80.0.3987.106 Safari/537.36

OK after mapping /data and /plugins folders outside of docker container, I’ve tried manual install of Calendar plugin.
For some reason it says plugin incompatible, even when Kanboard version match

config:

Any ideas what else could cause incompatibility?
Thanks