I would begin by not overwatering. Gnats only thrive on decomposing, wet, organic material. If you have a dirty spot with lots of leaves on the floors, etc. Its time to clean up.
You really should only have to treat a few times as the life cycle of a fungus gnat is short.
Skip the bits and H2O2 drench. Go to Home Depot and buy a small bottle of Thuricide by Southern Ag. Its liquid BT, same as the bits. Once your victims have dried out a bit, do a drench with your new friend. Once it dries out again, drench again. Do this 3x over a week+.
This is the stuff: Amazon.com
Now, let’s talk about engineering controls. We have big brains and are smarter than those little specs of fly paper pepper!
Put out more yellow traps. These clean traps will be your lighthouse beacon. Replace them during your drench process to determine progress.
Keep soil around 90-100mbar. Not dry, not wet.
Warm your space if its cold. This can help you control your soil moisture.
Proper drainage! Line your pots with rocks, netting, or both. Consider a plastic pot stand if your pots sit in standing water!
With the battle! I know your close so just text if you have questions.