I tried to install Yuka through the play store. Was denied. I was able to install through Aurora store but on app start up a message was displayed saying I needed to download the app from the play store. So I sent a message to yuka and received the following reply:
"Thank you so much for taking the time to contact us and share your enthusiasm for our app! It means a lot to us!
We do use Google services to manage the users' accounts and ensure security in our system. There is no possibility to use the app without these services, I'm sorry to say.
I'll forward your request to our developer team to let them know that more and more people are using Graphene OS and would like to be able to use our app as well.
Once again, thanks for your message and your support.
Have a nice day!"
Edit: I do have the play store and services installed.