You're overthinking things.

HDMI 2.0 is the standard around which 4K exists. So, any display on the planet which has 4K resolution and HDR support in some form, must support HDMI 2.0 at the bare minimum with the 18Gb/s transfer rate that is associated with HDMI 2.0.

The slightly newer HDMI 2.1 standard may support up to a 48Gb/s transfer rate, and may support resolutions up to 8K. It may also support 4K video at 120hz and 240hz which is what a lot of gamers are looking for.

ALL THAT SAID:
The DLP chip used inside DLP projectors is the same across all manufacturers. They have a few different models to choose from that Texas Instruments offers them, but they are most often using the .47" DLP chip inside all models. This chip is what Optoma uses, it's what LG uses. There is a larger .67 (I believe) variant, and a even newer .65" variant, but those are far less often used. Most of the time it's the .47" chip. This is what is in the smaller lifestyle models like the Hisense C1, and it's what is in almost all of the ultra short throw 4K models out there.

Not ANY 4K DLP projector supports 4K/120hz. That's a limitation of the chips themselves. Because they aren't native 4K, but are 1080p pixel shifting chips instead. They operate at 240hz to create a 4K image from 1080p resolution. But, they would need to operate at 480hz to hit 4K/120hz, which none can do at this point. So, HDMI 2.1 is an incredibly stupid and vague term. HDMI.org actually says that ALL displays today, if they have HDMI on them, should actually be called HDMI 2.1. If that sounds stupid, it's because it is. If the lack of any specific requirements associated with HDMI 2.1 sounds stupid, it's because it is.

What does 24Gb/s even add to the projector? Nothing. It's stupid.

But, specific to the UHZ66, it most definitely supports 4K/60hz resolutions and lists them on page 54 of the manual...
https://www.projectorcentral.com/pdf/projector_manual_12225.pdf

This includes 3840x2160 (4K) at 24, 25, 50, and 60Hz.

This is very typical and common for all of the 4K DLP projectors out there.

A couple of DLP projectors do have the ability to ACCEPT a 4K/120 signal, but they convert it to 4K/60 on the output or drop it to 1080p/120hz on the output. They can't actually display at 4K/120hz. Not any of them.

Only the Epson LS12000 or the JVC projectors can actually display at 4K/120hz.

The LG has much better contrast than the Optoma, but lower brightness. The LG also has better out of the box color accuracy. Optoma tends to incredibly overstate their brightness numbers and tends to have much lower brightness once calibrated. They have also been plagued with very poor reliability and service issues in recent years. A trend I am really hoping they get themselves out of.

The real plus with the Optoma is that it is using the 2x shifting .65" DLP chip inside of it as stated over at AVS Forum....
https://www.avsforum.com/threads/optoma-uhz66-compact-4k-laser-dlp-4000lm-500k-1cr.3287377/

So, it should have better reliability than many of their other models.