The bryntum_gantt_enterprise module attempts to load font files from bryntum_gantt/static, which results in a 404 and missing font-awesome icons.
This is reproducible on odoo-gantt.bryntum.com. Screenshot below.
As a temporary workaround, I have needed to create a very skeleton module that comprises nothing but the font files, effectively:
bryntum_gantt
├── README.rst
├── __manifest__.py
└── static
└── gantt_src
└── fonts
├── fa-solid-900.55b416a8.woff2
└── fa-solid-900.73820155.ttf