How to create managed metadata service in SharePoint Online for creating a separate term store. Is there any powershell script as i cant see any out of the box option in admin centre.
Why do you need a second term store?
I don't think that's possible. It wouldn't fit in Microsofts strategy with SharePoint Online. SharePoint Online is a very standardized product in terms of system architecture and backend services.
But I don't know for sure, though.
You cannot create a second term store. Your default term store’s name is a random string of text. The reason to me is clear, but documentation from MSFT is lacking. It’s clear to me that many admins are willing to create a multitude of term stores on prem rather than reorganize and possibly break existing ones. Consolidation of these term stores when migrating to Online makes a lot of sense since the future of SharePoint Online is ‘modern sites’. As such, the only way to have consistent navigation across the tenant is to utilize managed metadata navigation.
It is OOTB limitation of SharePoint Online ( rather i would say it is by design due to multi tenancy structure). In your scenrio, you have to plan it and merge both MMS applications into single term store. I would test with the tools or whatever method being used for migration. Only testing of different combinations will help and make migration successful.