Most Organizations that had adopted Copilot for Microsoft 365 has this dilemma on when to extend and when to build Custom Copilots, both options provide benefits and choosing the right approach provides enhanced productivity features as desired.
Having the fundamental understanding of each of the available options will help you decide the suitable option and you have related guidance from Microsoft with various options to extend or build your Custom Copilots.
Recently Microsoft team added a new MS Learn module to help you understand how you can extend Microsoft Copilot for Microsoft 365 with Copilot Studio.
You can access the learning path here: Extend Microsoft Copilot for Microsoft 365 with Copilot Studio
Also register for the Upcoming Microsoft Adoption - Customer Hub Sessions on Copilot for Microsoft 365 Extensibility scheduled in coming Months and on demand to know more.
Register here: Copilot for Microsoft 365 extensibility