Old 26'er with a rotted chain, quill stem, rim brakes, and the break lines are probably rotted in the tubes? Honestly go for it, my "first" bike was an old hand-me-down just like it and it got me through dozens of miles of trail once fixed up. There are probably much better bikes for a few hundred on fb marketplace, but if your goal is to learn on a budget then you're already halfway there! I would recommend some penetrating oil though..

Edit: curious about the bright pink sprocket, also we can't see if the crank or cassette are badly shark toothed, but if they look like Jaws you may want to consider another bike