First off, welcome to the world of photo! It's a slippery slope in a good way and bad. It's good in that you're going to become obsessed with images and composition, and it's bad because there's so much fancy and fun gear and you're going to want to try it all.
My advice would be to start small. It's so, so tempting to read reviews of gear and get swept up in making your first camera purchase a big one because hey, if you're going to get really into photo, you might as well start big right? That's certainly one way to do it, but I'm an advocate of learning what about photo you like the most first, then building up from there. Especially if you're mostly going to be posting on social media, it's better not to get caught up on megapixels or sensor sizes.
Dr.McCoy made a good point in starting with whatever's available to you. Phone cameras are ridiculously good now, and are the perfect tool to practice composition and how to look for the best light. Once you feel like you need more control over your settings, I think moving to compact mirrorless is the way to go. They're light and portable, and many of them are able to be set to full manual.
DSLRs are fantastic machines, but they are big, heavy, expensive, and you may not like the attention they bring once you whip them out (i.e. Uncle Joe sauntering over with his Nikon D850, trying to chat you up about the latest greatest lenses he read about online.)
All in all, just have fun and enjoy it. Read up on how to improve your photography, practice it, and learn to edit. Most importantly, find what works for you. I started with a Nikon D90 DSLR, and I didn't discover how much I really loved shooting until I bought myself a little compact mirrorless Fuji X30. That heavily impacted my next purchase for my next camera which I know will be with me for a long time.
Lastly, invest in your lenses, not the body. The sensor plays a role, but your lenses are what will truly make your images shine!