Why would working on ads be any more meaningful than my current job, even if it's using ML?
We can't answer this for you and really nobody should try since you didn't provide any areas of your life that you find meaning in or industries you'd be interested to work in.
Most jobs out there aren't going to have any meaning and the ones that do wont don't pay as much as you want since you've indicated in other comments that pay is important to you.
Heres what I'll tell you. Accept the fact that most jobs you have and most jobs everyone have are meaningless, put your 30,40,50 hours a week in at your current job and find meaning outside of work and just realize that work is a means to an end.
Or, quit your current job, find something remote realize that you'll probably take a pay cut but with that you might be able to get a reduction in hours that you can spend more time doing what you want and be back in your home town with your family.