Could you please clarify where the information regarding the project’s budget is detailed, in particular for the Call for proposal on Governance Projects?

All the information concerning the budget are in the Programme Manual (page 25, Drawing my budget).
Indeed, the Terms of Reference contain only the specific information related to the Call while common items to all calls are detailed in the Programme Manual.
In addition, concerning the Call for proposals on Governance projects a technical meeting on the eligibility of expenditure and budget was held on the 31st of March. The recording and the agenda are published on line :

Finally, the global budget for TCPs (Interreg funds + national co-financing) is 20 000 000 EUR. Total budget per project should not exceed 5 000 000 EUR.
The global budget foreseen for IDPs is 16 000 000 EUR,/ Total budget per project should not exceed 4 000 000 EUR.