If you mean the fact that it's not ribbony, with a lot of unused empty space between widgets and with mobile-phone-like aesthetic - the rejection of that style is intentional. Microsoft went that way, and hurt usability; LibreOffice has not. Although some argue emphatically that it's the way to go in order to attract new users.
For those who like a more ribbon'y UI style - it's available as an option. On the menu, choose "View > User Interface..." TBH, that's not fully-developed and I don't like it much.
One other aspect of modernization is that there is a dark mode, which has improved a lot over the past couple of years: https://itsfoss.com/libreoffice-dark-mode/
but if you have specific suggestions/rants - UI/UX discussions are always ongoing, albeit slowly given the immense size of the project and the amount of dialogs and UI/UX aspects to be considered and improved. Try the "LibreOffice Design" channel on Telegram for example.