If you insist on 'secure' firmware, you're fighting uphill and probably going to be disappointed with the ecosystem out there. Tunnel back to your home network to access cams if that worries you.

I recommend either Ubiquiti or Reolink cameras, both are power-over-Ethernet. Both offer an app that allows connecting back to your equipment. UI will require their Protect software running on one of their local platforms in your house with storage on 1 or more disk drives, while Reolink offers direct storage on microSD on the camera itself, capped at 256GB.