Editor under iOS
Under iOS - and with iPhone 12 :

1 - the first letter and the "..." menu are overlap 2 - every new line is double or the interline is 2x
For other question I am always available.
- is fixed in https://github.com/nextcloud/text/pull/1710
Changed the issue description to refer to the remaining part of the issue.
I think #2775 will fix this. What's happening here is that enter was always understood to mean start a new paragraph. Having a bit of spacing between paragraphs is to be expected. shift+enter would create a hard line break without a new para. However there was no way to create this on mobile.
The PR makes it so that one time pressing enter will create a hard line break - with a normal distance between the lines. Pressing enter twice will create a new paragraph. This behavior will only change on mobile.
Yes, with the current implementation this is expected behavior, so lets close this as a duplicate of https://github.com/nextcloud/text/issues/2761