The main difference is front-end developers are technical persons whereas UI/UX designers are non-technical persons. Developers need programming knowledge of HTML, CSS, and some tools for developing a product whereas designers just need what users want, how they want the product, and how to provide a smooth experience to the users.
Yes, these positions will overlap. In startup companies, due to a lack of people, both work will be done by a single person when it comes to top companies they have both front-end developers and UI/UX designers to do the work.
Both these fields are providing ample opportunities. Well according to me it is better to go with UI/UX designing because anyone can learn this technology just it needs interest in this field. If you are looking forward for a place to master this tool I recommend you to go for the Intellipaat UI UX design course where the course is designed in such a way that anyone can learn it easily from basic to advanced level.
For your reference, I am attaching a complete UI/UX free video from Intellipaat do check out this -