You don’t want as many employment opportunities as possible. You want an appropriate range of employment opportunities that you will find enjoyable on some level. It doesn’t matter if there are 20x as many openings for electrical engineering majors if you have no interest in being an electrical engineer! Focus on quality, not quantity.
Also, I think you should focus on career and type of job, not company. When I hear you saying Tesla or SpaceX, what I really hear is that you want to work for a company that is on the cutting edge in science and engineering. Maybe you want to be involved on the edge of discovery, and that’s exciting. But remember that Tesla and SpaceX - being large companies - also hire positions like accounts, lawyers, business managers, etc. Tesla’s current openings have tons of engineering positions but also lots of positions like account manager, HR business partner, inside sales, inventory analyst, legal counsel, logistical analyst, operations analyst, real estate advisor, and recruiter. Some of these positions - like data engineer, operations analyst, and reliability analyst - explicitly ask for a math degree, and some of them require no specific BA or BS, just that you have one. SpaceX, similarly, has lots of engineering positions but also jobs in business management, corporate communications, HR, and supply chain management. Lots of tech companies hire math and physics majors on to analyst or program management positions.
Do you simply want to work at an innovative scientific company, or do you want to do innovative scientific work? Even if the latter one is the answer, you can certainly do that with a math and/or physics degree. You’d probably eventually need a graduate degree in a math or physics-related area if you wanted to do R&D. But you could start out with a BA or BS and work for a few years first before earning the MS.
Also keep in mind that Tesla was founded just 13 years ago (and really didn’t enter the public consciousness until maybe 5 years ago) and SpaceX was founded around 14 years ago (and, similarly, didn’t enter the public consciousness until much later). They are young companies. The hot new company of the future doing innovative stuff might be something you haven’t heard of today, or that may not even be founded yet.