A rewrite is emotionally clean and operationally dangerous. The strongest modernisation programmes change the economics of the platform in deliberate slices.
Modernise around value streams
Map the customer and operational journeys that create value. Then identify the architecture, data, and team boundaries that make those journeys slow or expensive. This produces a sequence the business can understand and fund.
The aim is not a newer stack. The aim is a business that can change direction faster, serve customers more reliably, and spend less energy keeping yesterday alive.