Lubuntu 21.04 Install BIOS start disk partition GPT requirement 8 MB unformated partition

Is possible install Lubuntu 20.04 in BIOS using disk GPT if creating an partition /boot and grub in MBR.
The system start correctly.
Now Lubuntu 21.04 show message about “need to create an unformated partition 8 MB” to start GPT disk in BIOS.
Lubuntu 21.04 start correctly without problems if only creating partitions /boot and / and grub in MBR or a unformated partition 8 MB plus /boot and /

what is the because the unformated partition need to be 8 MB ? minimum ext size or grub files size ?
only care if in future updates or upgrades the unformated partition size need to be above 8 MB because resizing the first partitions to change the unformated partition size is an long time thus an value above 8 MB is better choice ?
thanks for reply.