When opening a form in tab view, is there any way of pulling the form to fit the window?
At the moment, no. This has been the center of some discussion in the recent past (especially when changes caused Detail and Form views to have different widths).
Keep in mind that AppSheet is a “Mobile First” platform. This is an industry wide mantra describing apps that are primarily designed for mobile devices. The design going into browsers on desktops is secondary and most vendors try to keep a consistent behavior. Hence the reason why the browser keeps the width on Forms like it does.
AppSheet did report in recent past that there is development focus on the Desktop view designs and gathered a ton of input from various Community posters. This was in recognition that many apps are being designed primarily for desktop use. AppSheet has made some small steps in this direction but there haven’t been significant changes yet.
It wouldn’t hurt for others to chime in here to help AppSheet gauge the continued need for desktop design improvements and possibly an update where that stands on the list of work.