To make the marinade: In a stainless-steel bowl that will fit in the Instant Pot, combine the lemon juice, ginger, garlic, chili powder, garam masala, turmeric, and salt and stir to mix.
Add the salmon to the marinade and turn to evenly coat with the spices. Set aside.
Select the high Sauté setting and heat the oil. Add the onion and salt and sauté until the onion turns translucent, about 5 minutes. Cover the pot with a glass lid (or other nonlocking lid that fits) to speed up the process. Add the ginger and garlic and sauté until aromatic, about 1 minute. Add the tomato puree, chile powder, turmeric, and garam masala. Press the Cancel button to turn off the Instant Pot. Pour in the water and stir well with a wooden spoon, nudging loose any browned bits from the pot bottom.
Place a tall steam rack in the pot, making sure all of its legs are resting firmly on the bottom. Place the bowl of salmon on the rack.
Secure the lid and set the Pressure Release to Sealing. Select the Pressure Cook or Manual setting and set the cooking time for 4 minutes at high pressure.
Perform a quick release by moving the Pressure Release to Venting. Press the Cancel button to turn off the Instant Pot. Open the pot and, wearing heat-resistant mitts, remove the bowl of salmon to a trivet and remove the rack.
Stir the heavy cream into the curry, then crush the fenugreek leaves with the palms of your hands to release the aromas and stir them in as well. Select the high Sauté setting and carefully add the salmon to the curry, turning it to evenly coat. Cook until the curry comes to a gentle boil and is heated through, 2 to 3 minutes. Press the Cancel button to turn off the Instant Pot.
Spoon the curry onto plates and serve the rice, naan, and lemon wedges alongside.