Modeling a system with logs

I am planning a solution that will only use mongodb to store data.
I am thinking about how to implement an action log system, that is, every CRUD action must have a log containing the user who performed the action, so that a super user of the system can do an audit in the future. For example, imagine a “customer” collection, any and all actions that happen in that collection must be recorded, for example, if any system operator changes the customer’s name or phone number, the change made and who made it must be recorded.
I thought of two ways to do this, the first is to create a separate collection to store these logs, the problem with that is that I think I would be obliged to work with transactions, the other way would be to insert additional fields in each document, informing which one was the last action taken, the date and time, and the name of the operator who made it. In that case I would have to make changes to the domain classes to add the new fields
Which of the two ways would be most recommended?