Name an owner
One name per system. Not a team, not a committee, a name. The cheapest control in the whole modernization toolkit.

Name an owner. One name per system in the inventory. Not "the platform team". Not "shared". A person, with an email that answers.
Every estate we walk has between five and fifteen systems owned by nobody. You find them by asking "who do we call when this breaks" and watching the room look at the ceiling. Those systems are where the migration schedule goes to die, because every decision about them requires a meeting to decide who is allowed to decide.
The fix costs a spreadsheet column and one uncomfortable hour with a org chart. Assign every row. The owner does not need to understand the system yet; they need to be the person who signs its retirement papers or its upgrade budget. Understanding follows signature. It always has.
Two rules from the field. If someone owns more than eight systems, they own zero of them; split the load. And the system everyone is afraid of goes to the most senior volunteer, publicly, with the fear written into their objectives. Fear that has an owner shrinks. Fear that floats grows.
Do it this week. It is one column.