FreshRSS - Not too big on RSS, but for me it does the job. Also, If I understood correctly there is an Open API so you can use another Client with FreshRSS Back End

https://github.com/FreshRSS/FreshRSS

I don't think so, but you can find a list of apps compatible with it here : https://github.com/...

... Can't believe I've never thought about that, but now I'll never fail to notice... Damn it