Support for Sony A7iv ARW files?

You have correctly stated the Sony A7 IV camera. ARW is not a format, it's a family of formats because each individual camera has its own raw format. Only smart manufacturers do offer natively a public common raw format which is the raw DNG format. The DNG raw format is  read and understood by all versions of PSE. That means that when you buy the latest camera model, it takes time for Adobe and other software companies to issue a converter for the new format. When you subscribe to a Creative Cloud solution, you generally get an update for the ACR converter in a matter of a few weeks. With Elements, the ACR module is different from the full ACR for Photoshop and the program itself, not only the ACR plugin must be updated. That takes time and there may be no update for a given version, only for the next yearly version.

The official answer and explanations are in that faq.

https://community.adobe.com/t5/photoshop-elements-discussions/faq-will-photoshop-elements-work-with-my-camera-or-why-won-t-my-raw-files-open/td-p/4303022

So long as there is no ready update for the PSE ACR, your free solution is to use the free Adobe DNG converter to batch convert a full folder of your proprietary raw files to the raw DNG format which your old camera can read and edit. An additional  batch version, but free and with the same quality.

There is also a solution for recent PSE versions to manually update the ACR module for Elements.

https://helpx.adobe.com/photoshop-elements/kb/camera-raw-update-not-available.html

Be sure to follow the instruction carefully.