OptaneIconOverlay.ico sometimes always in temp folder

Do you have a 32Gb Optane module in your system, or was there one that has since been replaced with an SSD? I have a feeling the icon file is part of the Optane app to overlay folders you choose to pin to the Optane module for quick access.

The fact it is installed would suggest you do have an Optane module fitted, however you can safely remove the Intel Optane pinning extensions regardless, but do it through Programs and Features in control panel, or through Windows settings app.
It is possible that the Snappy utility merely detected an Intel hardware controller plus maybe onboard Intel RAID controller so installed the RST + Optane driver, in which case you could remove all the Optane options through control panel.
I would take the time to check if your system (since a pre-built) came with Optane as the abilty to pin folders for quick access could be useful to you, depending on your use case.

In Device Manager, open Disk drives. If Optane Module is installed it will show up there like in the screenshot below. Post a Screenshot. If no Optane is listed under Disk drives then may be as Pejole2165 opined "It is possible that the Snappy utility merely detected an Intel hardware controller plus maybe onboard Intel RAID controller so installed the RST + Optane driver, " May be your system is Optane ready.

Thanks for jumping in Jumanji, I know you have an Optane system so have more insight into the OP's issue than me.

is it safe to delete it?

Have a look at this Intel Support brief. Intel(R) Optane™ Memory Pinning in Windows* File Explorer Not Available...

On the face of it, it looks like an aberration created by a wrong or old RST driver installed by the third party driver application. Intel says with version 16.7 and above that OptaneIconOverlay.ico Extensions is not required and can be safely deleted if it still persists. It is more so since you do not have Optane in your system. However I would request @Pejole2165, my Guru, to have a look at it and give his opinion. (If Pejole2165 concurs and you do uninstall it with Win+X -> Apps and Features please make sure you create a system restore point, before uninstalling it)

If as stated in your computer specs you have DELL OptiPlex 9020, why on earth have you used a third party driver application to update rather than sticking to Dell Update or Dell SupportAssist? ( I have been updating the BIOS and drivers only with these OEM applications on my DELL Inspiron 3280 AIO. I would never ever take a risk updating with third party Driver update applications)