When saving a cell with long indented lines, the editor will inject a line break (and possibly whitespace). I found no way to avoid this change. Prettier is disabled.
In addition, trailing commas also get removed when entering line breaks. This is not great.
When editing a team notebook (which was the case here), only the team-wide Prettier setting is taken into account. Somewhat confusing (because not clear to the user), but very intentional (judging from the code).