ok might be visual only. Running apt upgrade should inform about the kept back package now.
root@DietPiProd:~# apt upgrade
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
Calculating upgrade... Done
The following packages have been kept back:
rpi-eeprom
0 upgraded, 0 newly installed, 0 to remove and 1 not upgraded.
root@DietPiProd:~#