layout – How to better improve the information density for long and complex forms?

How to format long and complex forms so that as many fields as possible are visible on the page, while maintaining readability?

I am redefining a business web application featuring a total of 30 fields on 5 sections when creating a quote and adding 10 to 20 additional fields depending on the business. state of the quote.

The customer has expressed a clear preference to see as many form fields as possible in each screen without having to scroll through the screen (this request seems reasonable but I have not tested it yet).

This is what the form looks like:

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My initial attempt was to introduce a clearer hierarchy and group entries into other subsections:

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But I think the UX could be further improved by moving the content in each tab vertically (and using the sidebar to present a summary) instead of horizontal + vertically.

Are there any other models that might be suitable here?

What other ways are there to keep a large number of visible form fields?