Is it possible for someone with the Term Store Admin role to access and modify the Global Term Store in the Admin console (rather than individual site collection term stores) without also being assigned a SharePoint Admin role?
The SharePoint Admin Role has much broader privileges than someone who's in charge of an organizational information taxonomy should necessarily have.
I think this is not possible to give access for just Term Store on Admin Center.
It is possible to give permissions to admin center with SharePoint permission management, but I wouldn't suggest to do that. I just tried out to give Contribute permission to admin center to a user and that user got permissions to manage everything on admin center without SharePoint Administrator role.