You need to update your version of the Adobe Camera Raw plug-in to at least version 13.1. Your Nikon Z7 II camera was released too late for it be included in version 13.0 which is the latest "official" release of Adobe Camera Raw for Adobe Photoshop Elements 2021.
However, version 13.3 has just been released and there is a "semi-official" workaround to install it which is described in this knowledge base article:
Phil, thanks for your help however I can't find the 13.1 raw installer. The link you gave me is for 13.3. I downloaded that and have no idea to install it - not computer savvy enough. I know it says where it was installed, but where is that? - rhetorical question only. Really disappointed, I have spent hours and almost $75.00 for something that does not work. But thanks again, Chris
Chris, you have spent $75 for a program that works perfectly fine with the raw files from your new camera that wasn't even released when Elements 2021 first came out. Yes, you need to follow a few instructions to update the Camera Raw plug-in, but were you able to use all of the features of your $3,500 camera without any effort on your part? Since you tell us that you are not computer savvy, I'm not sure what further response you want from us. Perhaps you can get someone who has more knowledge of computers to help you out on your machine. The instructions provided in the link given by Phil are fairly explicit.
I will assume that you are willing to work past your frustration and try the solution provided by Phil. So, here is a little further help:
You say that you have downloaded the ACR 13.3 file because you could not find the 13.1 link. (It is just a little further down the page.) Since 13.3 works perfectly fine with Elements 2021, there is no reason why you shouldn't install that version which is the latest update. The file that you downloaded should be named AdobeCameraRaw_x64_13_3.exe. Simply double-click on the exe file and follow the instructions that will be given you. Once you have gone through this install process, use Windows File Explorer to find the folders mentioned in the link and copy the Camera Raw.8bi file from the Creative Cloud folder (C:\Program Files\Common Files\Adobe\Plug-Ins\CC\File Formats) to the Elements 2021 folder (C:\Program Files\Common Files\Adobe\Plug-Ins\Elements 19\File Formats).
If you still can't figure it out, I suggest you contact Adobe Support. They may be willing to take control of your computer and perform this task for you. This workaround is an official one, but I'm not sure whether Adobe support personnel are aware of it. So you may face some resistance from them. Persevere and hopefully you will get hold of someone who can help you.
The only other solution would be to convert your raw files to DNG format using the free Adobe DNG converter. But if you are unable to follow the ACR instructions, the DNG converter instructions may not be any easier for you.
We're here to help you, but as the saying goes, it takes two to Tango.