I Don't see an option to create Plan under Plans section
Welcome to Atlassian Community!
Plans - it's premium feature, it's available not on all plans.
If your tariff plan includes Plans functionality, it's possible, that you don't have permissions to create Plans. It's configured in Jira permission settings, here:
https://your-company.atlassian.net/jira/plans/settings/permissions
Check, that your user group is set in "Plans User" permissions.
Can you add a screenshot of where you're trying to create the plan?
I can see the create option in the top navigation pane.
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