This is false. Reporting has slowed down as the hospitals have all been bombed. They don't use a "Google form", almost all of the infrastructure in Gaza has been destroyed by Israel during the genocide.
They later moved to a self-hosted form, which remains available to anyone who wants to report a purported casualty: https://sehatty.ps/moh-registration/public/add-order
This has been well known since early last year, when Hamas themselves spoke about their incorporation of these other sources.
Casualty reports slowed down presumably because the fighting slowed down; in any case it's not a reason to make assumptions about Hamas' methodology that are contradicted by easily verifiable facts.