Excellent, now you know your real problem; motivation, this is easily solved by thinking hard and deep on the one change you will like to see happen in the world(humans living forever, space travel, e.t.c), once you figure that one thing you want to see happen try and find a way to contribute to it even a little bit, motivation will come then.

You can either work normal jobs(preferable) and work part time on that goal or you focus mainly on trying to help see that change happen.

Takes things slow though and remember it does not have to be a grand goal or better you can try working on a very small part of a grand goal, for example if you are interested in climate change being solved you can help this happen by eliminating one of the bottle necks that people have to believing climate change in the first place; access to verifiable data, you can build a platform that collects this data from goverments and institutions around the world and make them available to the average Joe in visual parsable form.

Here is where that take it slow advice comes into play, also prioritizing all your interest in relation to your level of interest in them, your skill-set, and your network is definitely the key here.

It is either that you are definitely more interested in one than others or you are more suited skill-wise to another one or you are a 2nd degree connection with someone entrenched in another. One of these should come into play and be the deciding factor.

What happens if you have too many interests? There is too much to learn... it seems overwhelming

This _might_ be a sign of depression and/or burnout. If I may offer a suggestion, I urge you to seek professional help.

How to be motivated?