Replace Catalytic converter and P0420 still there

The fuel trim is bad - something is wrong there, and you do have to fix that. Without anything to work off of that you tried prior, I would install OEM oxygen sensors at the bare minimum to rule out junk data, and make sure you used the right one -- you may have put an upstream sensor in the wrong place, or vice versa. The next thing I would do is clean the MAF sensor out as well for good measure, or replace it - a MAF cleaner will likely be enough but if the code is sticky and you checked all of this and verified you have the right parts, I would change the MAF sensor. Work on the passenger side where Bank 1 is for now.

There is one other component you need to check: The HPFP. Smell the oil and if it smells like oil, the seal is failing and you will need to replace it.

If it continues with a code clear, something else is wrong. At that point I would check the ignition system just in case, but it is probably fine - so hold off on this for now. First thing I always do is rotate the ignition coils to see if the code moves, but clear it first. Once you clear it with the coils moved, that coil is bad - depending on how many are bad, you might just want to do all 4 or 6. If the code does not move, the spark plugs are suspect - do all 6, clear it, drive it and see if it comes back. If it does not, then the spark plugs were bad. If neither of these works, it's the cylinder head - there may be carbon buildup. You can try using something like Techron and do an Italian tuneup once you see the car is stable at low speeds, but once you see it is stable get it on the highway at 60-70mph for 20-30 minutes with mixed RPMs. As soon as you do this with Techron it tends to clear out a lot of minor clogs but if it's severe, you will likely need to walnut blast the cylinder heads. But the good thing is the italian tuneup will reduce the severity if it needs mechanical work done.

These newer cars are super sensitive about the performance of the cats, and O2 sensors. Did you use OEM Toyota cats and sensors, or aftermarket ones? If you didn’t use the Toyota OEM parts, then it’s usually due to the replacements not playing nice with the car. You really need OEM sensors and cats on the newer cars, sadly. It was fine years ago when the computers weren’t as touchy in the early 2000s, but not after the EPA (and governments around the world) got picky about how forgiving some of these ECUs were. For really old cars (think 90s-early 2000s) it isn't an issue but these new cars will never work right with aftermarket sensors*.

*If you’re in a no-inspection state, just accept the P0420 code if an OEM sensor does not help and the cats are bad ;). We do it a lot in these states anyway after 10+ years because of how expensive it is to TS the system. It's normal. Unethical? Probably. Illegal? Heh, nobody pays attention.

This car is one of those new-fangled whiny ones which IS very picky, so OEM is a must - yours is in the middle where it still is (kind of) forgiving. That said I suspect it is sensitive because it is a Lexus and Toyota in general has been sensitive to parts for years before the others caught up when the EPA and other world governments forced them to be less forgiving.