Issue Type = Question, as I don't know if I am dealing with lack of user education or confusing/buggy UI.

I'm kicking the tires on the T4 Framework using the T4 Blank template, Alpha 3 build (7/4/2019) loaded via Quickstart and updated to Joomla 3.10.

I am experiencing unexplained weirdness in trying to style the Main Menu. At smaller widths, two hamberger icons display. At the large width, the hamburger menu icon appears where the menu should display since there is sufficient width to display it. I suspect the T4 mainmenu module now has the conversion to off-canvas toggle built into it's code, so the block in the Blank template that has both mainmenu and offcanvas toggle in it's block code is causing redundancy. What I have not found is the setting that determines at which width the change occurs. If the change is meant to be automated based on testing the rendered width of the menu, the measurement does not seem to be accurate. The menu should be displayable at the Large width. If the width is being set, I am not finding a place in the UI that affects this other than the specific prompt to render on Small screens.

The behavior I would expect is that the designer can render a hamburger icon in a row and column of their choosing, and that the menu can be rendered in a different row and column of the designer's choosing and with the option to render as a horizontal or vertical menu. The breakpoint should be selectable using BS4 classes such as d-block d-md-hide. My impression is that the configuration of columns interface, Responsive tab, toggling of visibility at each breakpoint is intended to be setting and removing these styles, but I am seeing styles in the rendered code that do not match the settings. I'm guessing that by trying a breakpoint-related setting and then clearing it by matching the settings at smaller breakpoints is not actually clearing the setting, but is instead accumulating settings that are in conflict. Perhaps the "Reset" is not fully effective at removing all styles because even with a Reset, there are styles being rendered that I did not set, and there are styles I am placing in the CSS settings for a column that are not rendering. I haven't found the pattern yet, as the system is not consistent with my expectation of how it should behave and so this may be that there has been a redesign of the approach compared to T3 and I just haven't figured out how it is supposed to work.

I also tried to replace the hamburger font-awesome icon with an SVG animated icon, but found that the block file is not in the template folder at te same location that it was in for the T3 system. Is there any documentation about the new folder structure and the rendering sequence to better understand which class settings will replace or overwrite other class settings?

I also found that the template preview in the Administrator is not rendering the custom.css file's overrides and so custom changes are not visible in this view; it doesn't match the front end view. I consider this a bug, but can understand how in this context, rendering custom.css could have unintended consequeces affecting other parts of the backend editor.

I'm also unsure whether the Build Mega Menu switch still has any effect or purpose.

If there is a resource to understand the design intention of the T4 implementation of BS4 and best practices for using the template editor, please link me to it.
Any insights appreciated.