Is it worth the $3-5k for the facelift 2021+? Any mechanical changes that addressses any issues of the pre-facelift?
The changes between the 2018-2020 and 2021-2024 models are minimal and do not impact anything mechanical. Essentially updated alloy wheels and they changed the infotainment screen from being flush in the dash for the 2018-2020 models to a tablet-like version in the 2021-2024 models. To be fair, both run the same infotainment software which is horribly outdated.
Oh, and paint color options changed a lot between 2018-2024. It seems like Toyota added or deleted colors pretty much every year of the 2018-2024 run.
The 2018-2024 Camry has been pretty good so far. Not that there haven't been issues, but Toyota worked out most of the kinks pretty early on in the generation- so as long as you go for a 2019+ you should be fine. Honestly though, most 2018 models probably aren't bad either.
-Can the passive safety features be turned off? If yes, would I need to turn it off every time I start the car?
It would probably be best to read the manual for those features... you can download a copy off of Toyota's website.
I believe that some of the safety features default back to on when you restart, but several of them remain off if you turn them off. I'm pretty sure that the lane keep assist feature can be turned off (and will stay off) just by pressing and holding the button on the steering wheel for about three seconds. I believe that the blind spot monitoring system can be turned off via the instrument cluster display and will stay off. As for the automatic emergency braking- that one I'm not sure of.
The adaptive cruise can be changed to manual (old fashioned cruise) by pressing and holding the cruise button on the steering wheel for about three seconds.
-Are the pano roofs shattering?
No, they are not shattering. I'm sure that there's a weird case somewhere after someone's roof got hit by something- but they are not shattering without reason.
With that said, the panoramic sunroof that Toyota puts in the Camry isn't without its problems. The seals are prone to having problems and as R Bush above mentioned, there have been issues with the glass coming off the track. If you search the forum, the biggest complaints involve the seal between the front and rear pieces of glass and the fact that a few people have experienced a weird problem where the gloss black trim pieces in front of and behind the pano roof discolors after a few years from sun exposure.
Beware that the cost of repairing that sunroof can be obscene, again as R Bush mentioned. The good news is that unlike in 2018-2021 when Toyota didn't sell the individual parts separately, a lot of the parts for the pano roof can be ordered a-la-carte which makes minor repairs a bit cheaper (but still expensive). Also beware that Toyota's extended warranties generally do not cover seals or the faded paint problem. It would likely cover any mechanical or electrical problems that you might experience with the sunroof.
-Any common mechanical or electrical issues I need to be aware of? I assume the engine and tranny is shared with the Lexus platform?
Generally speaking, the 2GR-FKS V6 is a reliable engine with only a few flaws. The biggest one over the past decade has been an oil leak in the front timing cover. It impacts any Toyota that has the 2GR under the hood- everything from Camrys to Highlanders to RX350s. Not all of them leak, and not all of them leak bad enough to require repair. But if you do need to have it repaired, it can be expensive, as it's an engine-out job. Generally those oil leaks don't develop until the car has 60,000+ miles on it... and again, not all of them experience the issue.
The other issue that is becoming more problematic is the 8-speed transmission that Toyota uses with the V6. The UA-80 in the V6 Camry has a design flaw that makes it more prone to failure over time. Four cylinder Camrys use a different version of the 8-speed transmission and don't seem to be impacted- but V6 Camrys do use the problematic transmission. Like the oil leak, not everyone is experiencing the issue- and it's just starting to be discussed. That UA-80 problem is also happening in several other Toyota models. That issue alone would cause me to want to get an extended warranty on any V6 Camry.
I wouldn't necessarily let the two issues above prevent me from buying a V6 Camry. They are overall great cars and most owners are happy with them year-after-year.
With any used car purchase, it's always a good idea to have a trusted independent mechanic give the car a full inspection before purchase. Not everything shows up on Carfax- and the stuff that doesn't show up is generally what needs to be worried about the most- mechanical issues 'fixed' on the cheap or accidents that aren't reported and repaired by companies that cut corners.