who is legacy developer Hp

Probably Hewlett Packard (aka HP). If you once had an HP printer or scanner that you no longer have, look in the Library/Extensions folder for any HP extensions and if found delete them and restart your Mac and see if the problem reoccurs.

Regards.

It's Apple's way of telling you that there are changes to the OS in the foreseeable future that will compromise the ability of that system extension. You may install it now, but it may not work after a future OS upgrade.

About system extensions and macOS - Apple Support

If you still have an HP printer, then you probably need a newer version of their software. Contact HP Support for further assistance.

Regards.

but I still have an HP printer. Does that mean it will no longer be compatible?