I have found an issue when editing my flows using the new designer, when I have a required Yes/No (Boolean) field in an Update Item action using the SharePoint connector.
For example, I have an Update Item action on a SharePoint list with a Choice column called Last risk. In the old designer this shows correctly as not being changed:

When I open the same flow in the new designer, the action now shows the field being set to Green (the default value):

In another example, I have an Update Item action on a SharePoint list with a Yes/No column called Active. In the old designer this shows correctly as being set to No:

When I open the same flow in the new designer, it now shows the field being set to Yes (the default value):

I far as I can tell, this is a bug in the new designer, which is silently altering the action field mappings. I have lots of complex flows and this has already caused an issue for me after I made a small change to an action (not the Update Item action) using the new designer, and then found that some fields in my SharePoint list were now being reset by the flow to their default value.
Has anyone else seen this issue and is Microsoft aware of it?