Please kindly refer to following information for further reference.
VLAN scenario:
The member ports of VLAN 2 group from two FGSW-2624SF can communications with each other, through the Uplink port 26 (Tagged with PVID 1).
VLAN setting:
1. The same IEEE 802.1Q VLAN setting on both FGSW-2624SF, please choose "802.1Q" in VLAN Operation Mode and we can see default VLAN 1 group include all ports with untagged and PVID 1.
2. We add a new VLAN 2 group, and then assign port 1, port 3, port 5 with Untagged and port 26 with Tagged as member ports.
3. We assign PVID 2 for port 1, port 3 and port 5 and PVID 1 for port 26, then the port 1, port 3 and port 5 from two FGSW-2624SF can communication with each other through the uplink port 26 (Tagged with PVID 1)