Why does every program on earth no matter what it does thinks they need to use a subscription model?
The only time I think a subscription is agreeable is a service is being provided (email, storage, backup, etc) or the ongoing rapid development of the software is critical (password managers, etc).
But this can be replaced with so MANY free alternative the dev of this program should just opt for a small fee for a perpetual license and be thankful of that.
https://splashy.art/ (Mac, PC, Linux)
https://johnsad.ventures/software/backgroundswitcher/ (Mac, PC)
and many more just google “desktop wallpaper changer” + Mac / PC / Linux