can i use sfsymbols in my app?

From the SF Symbols web page:

All SF Symbols shall be considered to be system-provided images as defined in the Xcode and Apple SDKs license agreements and are subject to the terms and conditions set forth therein. You may not use SF Symbols — or glyphs that are substantially or confusingly similar — in your app icons, logos, or any other trademark-related use. Apple reserves the right to review and, in its sole discretion, require modification or discontinuance of use of any Symbol used in violation of the foregoing restrictions, and you agree to promptly comply with any such request.

Especially the symbols marked with the little i in the circle (i) are restricted.

no

Of course you can use symbols in the code for buttons, tab bar items… They are made for that.