Due to some web bug comment got deleted... Yeah I was saying IOS dev is a good field there are demands. You can move to different devices also like tv, watch etc.
And a same time spring boot is also a lucrative choice. Because lots of mncs heavily use spring boot.
I'll say pick one tech at a time. First go with IOS dev, be good in it, the reason I'm saying because it is easy to grab internship and job in IOS dev field. Most companies will take DSA round, take home assignment and IOS/Swift related questions.
Once you get comfortable you can move with backend