@TheAndrey: See the discussion at:
WinSCP looks weird in Windows Dark Mode.
(including links to feature requests, that you can vote for)

I am completely satisfied with the current interface of the application. The main drawback of Windows UI is there is no support for dark mode, not all elements change their color. According to this parameter, it is outdated.

Registered to say that Flat UIs are bad for desktop. Version 6 is a complete non-starter because of the visually destitute look-n-feel.

@jdran: Thanks for your feedback. Btw, we are working on more flat icons.

She probably means that the interface be a bit more eye pleasing. Design fundamentals have changed through the years. There have been several different design advancements, such as flat design, larger areas and buttons, etc.
I understand this can be a tedious work, and I don't have that requirement from you, but it would be a good idea to consider (or a checkbox to check) in the future.

Can you please be more specific? WinSCP uses classic Windows UI, as many other applications.

Hello, I contact you because it is now many years that I use WinSCP, but for me it may be time for you to make a complete overhaul of the interface a little more modern and pleasant to see :)

Sincerely