I have the same question as Arvi above.

I've made an example where some entries are typed in two different cells/rows, and some are just broken with the ALT+Enter to show up on a second line in the same cell.

In the first example where they are in two different cells, you can use a Concatenate formula to combine the contents of the two cells, and in this case, adding the comma and space in between them.

In the "Peppermint Patty" example, I used Find/Replace, and in the Find cell I typed a CONTROL+J, and replaced with the comma and the space. It eliminates the manual line break in the Excel cell.

Another method entirely if you have a lot of those line breaks within the cell would be to transform your document in PowerQuery if you have it. There's a command in there which would make it easy to remove those line breaks. I have PowerQuery within Excel 365 for Windows but I don't know anything about the Mac side.