Exactly. A belt won't help bad lifting form, which probably is your real problem.
That said, a belt is also not something you use to "support your back". That's not, contrary to bro science, what a belt is for. A belt is used to brace against, not support your lower back.
A belt should start out a touch loose and then, prior to lifting the weight off the floor or off a stand, you push out into the belt. You should, if you are doing it right, feel not just your belly pushing out but your sides as well.
That said, I'm not saying to not get a belt and use one. They will make lifting safer just from having your torso braced to avoid spinal shift. But if you don't use it properly you can do some damage.
Best belts to use are powerlifting belts, because they are designed for heavy bracing. Lever belt is so much easier and faster to use, once you get your lever fitted to the right holes in the belt. Some use prong belts, which are a pain to put on and take off, as they say they can make them tighter or looser just by choosing a different notch in the belt. But if you are using it looser or tighter in a workout, you aren't using it properly anyway. Just get a lever belt. End of story.
To fix your lower back, your back needs to get stronger. Try paused hypers for the lower back. Seated rows for upper back.