It's not just Qualcomm it's closed source driver blobs in general.
Even if your CPU might still be supported your other hardware might not. A common offender is camera drivers as far as I know and while you sometimes can still make the camera work it often comes with noticeable decreased quality (as the special patent encumbered closed source image post processing sausage is missing).
Besides that potential but as far as I know less likely offenders include the modem.
Ironically both might be integrated into the SoC which then massively increases the chance for problems.
Even if your CPU might still be supported your other hardware might not. A common offender is camera drivers as far as I know and while you sometimes can still make the camera work it often comes with noticeable decreased quality (as the special patent encumbered closed source image post processing sausage is missing).
Besides that potential but as far as I know less likely offenders include the modem.
Ironically both might be integrated into the SoC which then massively increases the chance for problems.