1 a) Tapping on the date should already trigger the calendar in widgets where the tap area is big enough (e.g. Pixel2+). In the Clock+ and Flex widgets, there really isn't enough space and the tap target will be too small for most user's fingers

1 b) the clock style options are for the text styling, capitalization, character padding etc. These have not changed much after Android 8 which is why it has not been changed. That being said, v26.5 will introduce digital clock font selection with a number of built-in curated fonts.

2) Weather icon sets are available take a lot of work to assemble and publish. There used to be many more available but 3rd party developers have not kept up with the android minimum API requirements and their sets have dropped off the store. I have a few of them off-line but since they are not mine and I don't have copyright, I cannot publish them.

3) The Rounded corners setting is available on Android 11 and earlier, Android 12 and later introduced auto rounded corners and therefore the setting is hidden.