A few things come up often enough to be worth stating plainly.
The Pi 4 or Pi 5 will not boot
A Raspberry Pi 4 stuck on a white screen, or a Pi 5 on a black screen with a blinking cursor, usually needs a bootloader update rather than a different image. See Update the bootloader.
The card shows a much smaller capacity afterwards
A 16 GB card reporting 31 MB is expected. We format the card in a way Windows and macOS do not display correctly. The storage is all still there.
The card is locked or read only
Full-size SD adapters have a physical write-protect switch on the side. Slide it away from the lock position and the card becomes writable again.