deb https://deb.debian.org/debian/ trixie main contrib non-free non-free-firmware
deb https://deb.debian.org/debian/ trixie-updates main contrib non-free non-free-firmware
deb https://deb.debian.org/debian-security trixie-security main contrib non-free non-free-firmware
deb https://deb.debian.org/debian/ trixie-backports main contrib non-free non-free-firmware
Looks all good. APT would have thrown a warning if there was a duplicate entry in a left *.sources file.
And no problem, not your fault that APT promotes this modernize command. IMO that is something to at first inform APT repo operators about, so they can adjust their docs/scripts etc, rather than promoting this command to local admins, which will in case end up with duplicates, as long as 3rd party repo instructions or installer scripts have not been updated.