Not available in any menu, only in the advanced toolbar - last icon in the HTML toolbar section. It's also not possible to add it to the menu with the menu configuration dialog! Don't know why. However, you can add Artistic Style to the menu manually.

If you do not have already created a personal menu configuration,
click on button Manage Menus at Advanced - Configuration - Toolbars / Menus - Management, enter a new name, i.e. "MyMenu" and click on SaveAs to create a copy of the current menu configuration (normally standard menu Advanced) with the new name "MyMenu". This new menu is automatically used now by UltraEdit. Close the configuration dialogs.

Now open file "MyMenu.mfg" in the directory of your ini (default is uedit32.ini). See help of UltraEdit about "INI File Selection and Advanced Settings" about the location of the INI file. See also UltraEdit INI file location.

Now add following artistic style line anywhere you want. My example adds it in the Format menu.
Note: If you add it at the end of a menu, you must use LM (last menu item) instead of M (menu item) and make previous LM to M. S is a separator line. & underlines A and the "Artistic Style" menu item can now be activated by pressing key A if the menu is open. No other menu item in this menu should have A as hot key.

Save the file "MyMenu.mfg" and close UltraEdit. Next start of UltraEdit the MyMenu.mfg is automatically copied to "ini-name.mnu" (default uedit32.mnu) and you now have the Artistic Style in the menu.

I should add, that I never used Artistic Style till now and don't know what this tool is for.