Unfortunately, PhotoRoom is not available as a Desktop app today. It's in our plans and we wish we could do it but our focus for now is really mobile.
That being said, you can first register on PhotoRoom web list beta here https://photoroom.typeform.com/to/I3ISXC if a website would work in your case. If it would work please tell use why in the chat.
Now, that you know everything about PhotoRoom web and desktop projects. I can give you a few tips to use PhotoRoom on your iPhone and post your pictures on desktop. In particular, if you have user a cloud service. Let's say you have a dropbox account on your desktop
-Create the photo in PhotoRoom (starting from your photo library, camera or dropbox)
-Instead of saving the Photo, tap Save to Files then Choose Dropbox and a folder that makes sense for instance "PhotoRoom_Exports"
-If you don't see Dropbox in the Save to Files, you check this post from Dropbox
-Your Photos will be automatically saved to your dropbox and sync on your desktop as you can see below: