Stuck on what to build next, how do you validate a problem [i will not promote]

Looking for some honest input from other founders here. I have been running a startup for a while now and I am at the point where I am seriously thinking about pivoting now. We have been trying to find customers for over a 6 months and it just has not clicked. Bit late I figured out. The reason we are not getting customers on board is that we did not validate the problem properly up front. With the small customers we talked to, the problem barely exists. It does show up with the big players, the MNCs, but getting an MNC onto a platform like ours at this stage is really hard, and pouring more into chasing that does not feel right. So now I am kind of stuck on what to work on next. I have tried a bunch of ways to find the next problem worth solving and nothing has really stuck. I even went digging through Reddit to spot a real pain point I could build around, and still came up short. For context, I am a software engineer with about 10 years in big tech. The one thing I am genuinely good at is spinning up a prototype fast, putting it in front of people, and then deciding to pursue or kill it quickly. That loop is my real strength. This time I want to execute differently. Instead of building first, I want to start with small, specific problems, validate them against a small cohort, and turn that cohort into my first beta users before building anything serious. The part I am struggling with is the front of that funnel. I do not have a good way to validate a problem, or even to find which problems are worth looking at in the first place. So if anyone has been on this same path, or has a way they find and validate problems before building, I would really appreciate it. Just trying to learn from people who have been through this.