Its probably just one fret that's too high causing all the buzzing
First, straighten the neck (using the truss rod) and then measure the string height. Next, you want to level the frets. With that done, your next step is to do a setup. That can include nut filing, saddle adjusting (including filing if it's an acoustic), and ensuring the string height is correct.
Not all guitars can be set up properly. Some are just too far gone, but you can make them much better.
Every guitarist should know how to do all this stuff - but so many don't. They either never do it and just deal with it, or they pay someone to do it. You can expect to pay $40 to $100 to have a guitar set up by a professional.
I've never done that stuff
If you learn how, you will enjoy your guitars so much more than you already do. It really only takes a few tools.
You want the fret rocker:
https://m.media-amazon.com/images/I/711wx6yi3xL.jpg
You want the straight edge I showed you, the one with notches.
You want a fret leveling beam:
https://m.media-amazon.com/images/I/81Ce2U28DsL._AC_SL1500_.jpg
And, you want some files - a variety of them, including a fret crowning file:
https://m.media-amazon.com/images/I/61rnCesjnWL._AC_SL1500_.jpg
Then, you want a regular file or two. And some needle files for the nut - but there are nut file sets you could buy.
Optional tools exist, like gauges to find the fret radius. I have ALL the tools! In fact, I showed you a cheap set that I purchased at one point, when doing my 'cheap guitar' thing.
But, you really only need some basic tools.
Also, superglue. Luthiers use a lot of it! They call it "C.A. Glue" but it's just a fancy name for superglue. You can use that to push loose frets back into place and glue them there.
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