Phone was working fine 10 days ago, then we turned it off and now it wont turn back on again bizarrely.

Battery was replaced 2.5 years ago (and had over 90% health life I believe)

Everything else was working fine (touch id, camera etc).

phone is in good cosmetic condition (been in case and screen protector most of life, see pics). There are two small shallow indents on the back (tried to show in pictures 7, 8 & 9)