currently it is not possible to add lld-generated custom graphs, or simple graphs from lld-generated items, to screens.
a method do do that i suggested here.

to add such graphs to a screen, a single screen cell would be changed. this cell would act as a container for all auto-generated graphs.
in configuration section, only the configured data would be seen, actual graphs would be only displayed in monitoring section.

it would be possible to add :

• graph prototypes
• item prototypes (which would be show as 'simple graphs')

edit : also see an idea in https://support.zabbix.com/browse/ZBXNEXT-1353?focusedCommentId=67672#comment-67672 to allow specifying them by regexp (thus on a device with lots of interfaces they could be split in individual screens)

when adding these to template screens, only prototypes from same template may be added.
when adding these to global screens, prototypes from any host may be added, and a host has to be specified.

when displayed, this area is populated with graphs without modifying action screen row and column count - sort of table inside a table.

for each such cell we may also specify column and row span.

we may also specify either row or column limit - inside that cell/area elements would be limited to the specified row/column count and additional rows or columns would be added as necessary (again, only inside that cell, not affecting the rows/columns of the screen itself).

this will probably be a new screen element, requiring xml specification and documentation changes.

should be extensively documented (with examples etc) to make it useful.