Although the Microsoft 365 role "Service Support Admin" should have permission to submit support tickets to Microsoft, per this official article: About admin roles in the Microsoft 365 admin center - Microsoft 365 admin | Microsoft Learn, users with this role can submit ticket form M365 Admin Center only, but they cannot submit Power Platform tickets from Power Platform Admin Center.
From official M365 documentation from link above:
Assign the Service Support admin role as an additional role to admins or users who need to do the following in addition to their usual admin role: Open and manage service requests, View and share message center posts, Monitor service health
When user with "Service Support Admin" role try to open Power Platform Admin Center, they have access denied. As far as they cannot open PPAC, they cannot submit any tickets to Microsoft from there.
When user with "Service Support Admin" role tries to submit Power Platform ticket trough M365 Admin center, they need to use improper classification/type of the incident, which causes wrong routing of the ticket on Microsoft side, therefore, this is not acceptable workaround.
Official documentation for PPAC (Get Help + Support in Power Platform - Power Platform | Microsoft Learn) is not listing "Service Support admin" role. Any other role, which has ability to submit Power Platform tickets, has more privileges and permissions in M365 than "Service Support Admin" role.
There are many other M365 roles provided with the ability to submit Power Platform tickets to MS, although it has nothing to do with Power Platform - for example: Teams Admin, SharePoint Admin, etc. Why "Service Support Admin" is missed?
In order to improve the security, and in order to avoid of assigning unnecessary privileges and permissions to member of support teams on customer's side, please, provide M365 role "Service Support Admin" with ability to submit Power Platform tickets to Microsoft from Power Platform Admin Center or re-enable option to submit Power Platform tickets from M365 Admin center.
Thank you very much in advance.