This will usually come in the form of a USB equipment which needs to be plugged into the PS4.
Many sites online talk about using PlayStation’s Remote Play to use a PS5 controller with PS4.
Altogether, it’s not a great way to game or use your DualSense controller.

Mayflash
Mayflash
Set up using an adapter can vary, but in general, the process is largely the same.
Getting your controller working will only take a few seconds.
Plug your adapter into your PS4 console via an open USB port.
Once plugged in, press thepairing buttonon your adapter.
Hold thePlayStation buttonand theCreatebutton on your DualSense controller to enter pairing mode.
You’ll see your controller start flashing blue when it’s in pairing mode.
This means that haptic feedback and adaptive triggers won’t work when using your DualSense on PS4.
Select thethree dotsnext to Play Game, then choose the PS5 version to download and selectDownload.
Note: This will only work with select digital game purchases.