Does anyone know the difference, technical or otherwise? When looking at OEM plus, they have no speakers for the JBL equipped 4runners, that I see, other than a new amp and an enclosure with a amp and speaker set up.
I would like to replace my speaker in my 2019 with theirs as they seem to fit easily with no mods, and are pretty good quality.
I have emailed them, last week. No response.

My 2004 Sports Edition has JBL system and speakers still good quality. My fifth gen Trail had basic Toyota paper speakers and those were awful from new. I replaced them with OEM+. I don't think JBL stuff is bad. If I was you I'd keep it.

Check with Crutchfield. I have Polk Audio speakers from them in my 4Runner, and I bought a Sony head unit and Infinity speakers from them for my son’s Corolla. You get all the necessary installation parts from Crutchfield.

Depending on your audiophile status, your needs will differ. OEM stuff, even JBL, isn’t as good as high quality aftermarket. High quality stuff is expensive, though.

I have installed high end stereos in 3-4 different cars, one that was full McIntosh. Their amps have .005% (not a typo) THD. I have a 100x4 amp in my 4Runner powering a relatively basic, but modern, Clarion head unit and the Polk Audio speakers. First time passengers in my 4Runner are usually amazed by the volume and sound quality of the stereo, if they care about that sort of thing.

I was curious as to why they had no speakers to replace the JBLs.
I am not a audio aficionado, but the unit in my 4runner is a T8, and quite frankly isnt bad, just not great.
I use the aux cable to my phone for Pandora (Not the best, like Tidal for example).
But compared to my 93 Vette with , decent stuff from back in the late 90s, this thing sux.
Vette has Rockford Fosgate, sony speakers, and JVC head unit ( 2 din, fit the car, not much to choose from then). It sounds significantly better with Pandora Premium.
So, I know the 4runner needs help, and was looking ot OEM Plus to start..
I know it needs much better stuff.. I will get it in due time. Reviewing many systems people have on a few forums..

I’m not aware that there’s a size difference between JBL and non-JBL speakers. My 4Runner had the JBL system. I didn’t deal with the separate tweeters or the center dash speaker, and just put 6x9 coax speakers in the front doors and 6.5 coax speakers in the back doors. I have a shallow Pioneer sub mounted in the factory cargo area location, but it’s not hooked up right now. I don’t notice that bass is lacking without it.

I've kind of searched for the same thing over in the past year. 4Runners with the Entire JBL package I believe have the same speaker dimensions as other models with the exception of the subwoofer. Where there's been confusion is what ohm the JBL system requires, and ensuring any changes of speakers have the proper high pass filtering so that they work as intended with the existing amp. Personally the JBL system sounds good, it lacks bass in my opinion, the sub is only 8" and not exactly Kicker/JL quality leaving it very inconsistent in handling low and mid frequencies.

With your head unit maybe they did the bypass so maybe you can replace all speakers without an issue, but I'd wait for the pros to chime in.

Has anyone upgraded their 2020 JBL sound system? The Subwoofer is a little weaker and wondering if anyone has replaced the stock amp or 8 inch sub in the back

I don't want to compare but instead I'd like to emphasize why JBL has a better sound projection. They have a speaker on the front and at the back and ensures that the speakers have perfect sound distribution.

The front and back of what?

JBL sounds better than regular because it has a discreate amp, sub, and tuned speakers. It's certainly nothing special, just better than regular Toyota garbage audio.