The main focus of Domain Driven Design is to put the business first. The rest of the application (database, rest, input-output) has to depend on business.

It would be good if you design this based on your business. So you could ask the business people which statement (1 or 2) sounds more natural to them. I would put the question to the UX expert as well. Not to the UI developer however.

Statement 1: User requests for change of 5 items together in one short. And we inform him which part of the changes were successful.

Statement 2: User has the ability to make 5 different requests for change. And we inform him about the result

If statement 1 sounds natural, I would choose solution 1 or 2. (Choice between 1 and 2 is depending on how your code is organized) If statement 2 sounds natural, I would choose solution 3

There are few minor questions that comes to my mind. They are

Question 1: If you user requests for something to be done, it would be fair to let him know the status of his request. If the user request for some operation (update 5), and part of the operation succeeded, how are we going to tell him about the status? (It is possible to inform about partial success of a request in REST, but its complicated)

Question 2: If you decide based on your business that "these are better organized as separate operations (commands)". Then you would have 5 different commands, and have 5 commanding mechanisms in your UI. May be at this stage you could inform the user if he has the rights to perform each of the command or not (probably by disabling/enabling the command). There is a possibility of doing this by a ready model

The main focus of Domain Driven Design is to put the business first. The rest of the application (database, rest, input-output) has to depend on business.

It would be good if you design this based on your business. So you could ask the business people which statement (1 or 2) sounds more natural to them. I would put the question to the UX expert as well. Not to the UI developer however.

Statement 1: User requests for change of 5 items together in one short. And we inform him which part of the changes were successful.

Statement 2: User has the ability to make 5 different requests for change. And we inform him about the result

If statement 1 sounds natural, I would choose solution 1 or 2. (Choice between 1 and 2 is depending on how your code is organized) If statement 2 sounds natural, I would choose solution 3

There are few minor questions that comes to my mind. They are

Question 1: If you user requests for something to be done, it would be fair to let him know the status of his request. If the user request for some operation (update 5), and part of the operation succeeded, how are we going to tell him about the status? (It is possible to inform about partial success of a request in REST, but its complicated)

Question 2: If you decide based on your business that "these are better organized as separate operations (commands)". Then you would have 5 different commands, and have 5 commanding mechanisms in your UI. May be at this stage you could inform the user if he has the rights to perform each of the command or not (probably by disabling/enabling the command). There is a possibility of doing this by a read model