Is Google Tag Manager a MUST?

Hi all, is using Google Tag manager a MUST for making sure that Facebook Conversion API Catches all of the audience standard events at 100%? Can you please share tutorials where its via GTM and WITHOUT GTM?

The sGTM allows you to log data and check if all events have been sent actually comparing this to your backend/CMS data, so it just simplifies the verification and customisation process.
But you can also use direct sending of events via CAPI and not use sGTM for that: Utilisation de l’API - API Conversions - Documentation - Meta for Developers