Validating and choosing business ideas

Hi all, after many years of corporate experience I have decided to dedicate my time fully on building a start up. I have done some structural trainings with the Lean Startup and Design Thinking so I have some idea of how to get started. However, I am struggling with picking an idea. I have no specific passion or skill set which I want to further develop, so I have been brainstorming potential problems (to solve) or services which I think might be useful to people. However, I am struggling with narrowing down my picks. Is there a way I can get feedback or help with discarding ideas which are not sustainable by, let's say, people who are more experienced and could identify flaws at an early stage? I don't want to waste my time on things which won't lead to anything and I would like to narrow down my ideas to a manageable number which I can validate with the techniques that I've learned. I am also considering teaming up with a co-founder, but I have no connections in my network, so if you have any suggestions on where to connect with entrepreneurs, it would be much appreciated!