Draw the separation boundary
Make every shared dependency visible and assign an owner.
SAP Carve Out Day One for separations where Day 1 has to work before every dependency can disappear.
Carve-outs become risky when shared data, interfaces, users and operational dependencies are discovered after the legal or commercial timeline is already fixed.
SAP Carve Out Day One for separations where Day 1 has to work before every dependency can disappear.
Make every shared dependency visible and assign an owner.
Decide what must be separated now, what can be temporarily shared and under which controls.
Test finance, supply chain, users, interfaces and reporting against Day 1 scenarios.
Treat temporary services and duplicated controls as work with an end date, not a permanent architecture.
The current problem, the outcome you need and what cannot be disrupted are enough to start.