Photoshop 2021 needs to have SSE4.2 instructions on the CPU to work

If you updated to Photoshop 2021 (version 22) and now it does not work, please, see this below

But before, Be aware that you can use and download multiple Photoshop CC versions and older ones. Here is explained how to Install previous versions of your Creative Cloud apps

New Photoshop 2021 system requirements

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[ Processor requirement Intel® or AMD processor with 64-bit support; 2 GHz or faster processor with SSE 4.2 or later ]

I have seen this information about the new Photoshop version 2021 it shows an error about program error and maybe it may happen that your computer may be old enough that it does not support the SSE4.2 instructions

And this is the error that will show if you do not have the SSE4

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When you launch Photoshop 2021 (v22.x) you get the following error: "Error at loading of ippCV library." Photoshop 2021 (v22.x) requires a CPU that supports SSE 4.2 or later. To determine if your CPU meets this SSE version support requirement, see Photoshop's Help > System Info dialog and look in or near the 4th line to see this System architecture: Intel CPU Family:6, Model:14, Stepping:3 with MMX, SSE Integer, SSE FP, SSE2, SSE3, SSE4.1, SSE4.2, AVX, AVX2, HyperThreading

I have seen this whole thread in the Adobe Feedback forum about this topic of the new Photoshop 2021 to help to the ones that may have this problem

Adobe official feedback - Photoshop: Error at loading of ippCV library

Here is more

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Anyone with an old computer (either PC or Mac) may be disappointed as Photoshop 2021 (v22) won't run on a CPU that doesn't include the SSE 4.2 instruction se t. There are also some more recent low cost CPUs that don't have it. To find out if your computer has what is needed, simply run your existing Photoshop, go to the menu: Help, then System Info, and the fourth row down says "System architecture:". To the right of that is a complicated string, and what you are looking for is "SSE4.2". If you see it you are OK. If you don't then you won't be able to run Photoshop 2021 without getting a newer computer.

and this other comment

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There is a major problem with the Photoshop upd ate. Many people are complaining about a startup error, which apparently has to do with the computer's processor: the CPU has to support SSE4 instructions. Many (me, among them) use computers with some years on them, so we either upgrade, or we keep the old version of Photoshop

An even weirder problem. I also have this SSE 4.2 isssue, HOWEVER, my processor shows as having it, as demonstrated by the system information in Photoshop 2020. Yes, it's an old AMD Phenom, but it should work in PS 2021 and beyond, but I can't go beyond this version, apparently. I, too, get that error mentioned above when I try to update my version. This version, however, works fine. Is it possible that it actually SHOULD work fine, but, for some reason, my processor isn't on the approved list? Is that the reason, a mistake by Adobe when they made up the approved processor list? So, what's the real reason for the error, Adobe?
See the fifth line.

Adobe Photoshop Version: 20.0.1 20181029.r.41 2018/010/29: 1197484 x64
Number of Launches: 39
Operating System: Windows 10 64-bit
Version: 10 or greater 10.0.19041.3570
System architecture: AMD CPU Family:15, Model:4, Stepping:2 with MMX, SSE Integer, SSE FP, SSE2, SSE3, SSE4.2, AVX, AVX2, HyperThreading
Physical processor count: 4
Processor speed: 3211 MHz
Built-in memory: 16382 MB
Free memory: 10491 MB
Memory available to Photoshop: 14987 MB