Thanks for the new error messages and sorry for the late reply.
Can you please try the following steps:
systemctl stop mattermost
cd /opt/mattermost/plugins
rm -r com.mattermost.plugin-channel-export
tar xf ../prepackaged_plugins/mattermost-plugin-channel-export-v1.0.0-linux-amd64.tar.gz
systemctl start mattermost
Then go back into your system console and try to enable the channel export plugin.
If that helped, we can also do the same for the playbooks plugin.