Can the Microsoft Defender portal show the server details as per security group?

Yes — this is exactly what Device Groups + RBAC are designed for in Microsoft Defender (assuming you're managing these servers through Defender for Endpoint, which is the typical path for cross-vendor server monitoring).

The model:

• Device groups are the scoping unit (not Entra security groups directly) — create one per vendor/company (e.g., "Company A Servers", "Company B Servers"), using a matching rule (tag, OS, name pattern, etc.) to auto-assign devices.
• RBAC roles then get tied to an Entra security group and granted access to only specific device groups. So: Company A's people go in an Entra group → that group is assigned an MDE role scoped to "Company A Servers" only → they only ever see those devices, alerts, and incidents in the portal.
• You as admin keep your existing Global Admin/Security Admin role (or get added to both device groups' RBAC scope), so you retain visibility across both.

Path: Settings → Endpoints → Permissions → Device groups to create the groups, then Permissions → Roles to create a role and tie it to your Entra security group with that device group as the scope.

One thing to verify before committing to this design: this RBAC model affects what shows in alerts, incidents, advanced hunting (scoped automatically), and inventory — but make sure nobody from Company A/B also needs organization-wide Defender features like global threat analytics, since those aren't scopable the same way.

If you're actually talking about servers monitored via Defender for Cloud (Azure subscription-based, not MDE-onboarded), the equivalent mechanism is Azure RBAC at the subscription/resource group level (assign Security Reader scoped to the RG containing Company A's VMs) — different mechanism, same outcome. Worth clarifying which portal/product this is so the right one gets recommended.