Update-Faulty Cable-Replace and issue resolved.
The Dell Inspiron 16 Plus 7610 has a Thunderbolt 4 (TB4) port; the user guide / specs claim that (TB4) supports two external 4K displays and is backwards-compatible with TB3. Alas, I am unable to connect *two displays* over a proper Thunderbolt 3 docking station, with two DisplayPort output ports. I suspect a system BIOS and/or PCI wiring issue related to the mux between the Intel iGPU and the Nvidia dGPU of this specific laptop configuration. This specific Thunderbolt 3 docking station and external screen configuration works fine with a Dell XPS 13 9360 (over Thunderbolt) and a HP ZBook 15 G4 (over Thunderbolt, as Nvidia Quadro M2200 dGPU). Steps: //exp: two screens light up and are operational//act: only one screen lights up Unplug Thunderbolt cable, plug into Dell XPS 9360 - works. Unplug Thunderbolt cable, plug into HP ZBook 15 G4 (Nvidia Quadro M2200) - works. Unplug Thunderbolt cable, plug into Dell 7610 (Nvidia RTX 3060) - does not work The Dell software stack is fully up-to-date (from BIOS 1.7 to Windows OS to Dell Update drivers at the time of this writing). Let me stress that I am talking about two external screens via TB4 and a proper Thunderbolt docking station, not connections via DisplayLink. As an additional data point, I tried this in Linux (Fedora 36), too. Again the XPS 13 9360 is totally happy; the Inspiron 16 Plus 7610 shows only one display connected via Thunderbolt.
TB4 docking broken two external screens - Inspiron 16 Plus 7610 (RTX 3060)