It's fine. Just don't let it take over you and make you feel like it's not worth your time to draw anything else. I cannot stress this enough. This is an actual thing.
When started out as an artist I had several groups of artist friends (both online and off) that all drew original content, comics and the like, had goals to make their own comics and series and were working towards that, and of course, because they liked to and because it would hopefully help bring attention to their work, would work on some fanart on the side.
Unfortunately the 'bring attention to their work' ONLY worked for their fanart and NOT their original series, and they ended up only get attention for their fanart, and they were only able to push views to their fanarts online, and only able to sell fanart at conventions.
Eventually they all stopped working on their original stories and just switched to drawing fanart, because it got to the point where 'Spending time working on original content just wasn't worth it' Fanart is what pays their bills, and at this point... I wouldn't even call it fanart because most of the time they are not fans. Stuff like "I hate Sword Art Online so much, but it's what sells so I'm making some prints for it." or "I've never actually watched My Little Pony but these prints sell like crazy so I have to draw them." They're just not actually happy drawing the art they sell anymore, and they're so busy drawing things that other people will hopefully enjoy that they never have time to work on their own things anymore. Just fanart.
So yeah. As long as you don't fall into that hole I think fanart is fine!