Stm32 minimum setup no crystal
oh my, that's not an appropriate board layout. Glad I insisted on a picture!
Your ground return paths are nowhere near your supply lines, your trace layout is random, to put it mildly, and your decoupling caps are too few and partially not where they're needed.
Redo that design.

Put the capacitors directly adjacent to the supply pins. No exceptions.
Bottom plane is a ground plane, no exceptions, no signals running on bottom. You don't actually need both layers to lay out the traces for a schematic this simple. Even in a much more complex schematic, keep the bottom side clean and only use it as a ground plane, because you need that to carry high-speed return currents.
I don't know what happened to your traces, but it looks you really made a sport out of putting them in random places, with random kinks, and unnecessary bends and detour. Don't. This introduces problems. Do the straightest (vertical and horizontal only) shortest path from source to destination. Ground is not something you want to execute as squiggly trace that crosses sites. Even if this is a result of taking a complex board and deleting everything but the MCU, it wouldn't be good enough.