I am at a similar position but have not yet to started to actually look for a job. I am a 37 yo marketing guy and now I am learning to code to become a software developer (web). My approach is to take some time to learn the basics, create some projects that a potential future employee would recognize as demonstrative of my hard skills and then start looking.

When you talk about software development, this path is obvious, you can't do anything if you don't code. But even when there is no obvious hard skill that you can learn, I think you should try doing this way. Study, practice and create a portfolio of projects that demonstrate you are really knowledgeable about the topic. Don't expect any potential employer to trust that your skills are transferable and the new skills you will learn "on the job". Try to be as ready as possible to perform at the new role, not be hired as a promise.

Also, I don't believe 3 months is that long time to be discouraged and draw conclusions about why you are unemployable. Keep trying to check if that is actually the reality.

That said, I don't discard ageism or other reasons not related to performance to influence all the dismissions. It is possibly (probably?) part of the reason, but one you can't control. Except having some thoughtful arguments on why your age shouldn't be a problem, maybe even an advantage.

Good luck!