Hello，Normally a window that allows you to create or edit landscape would pop up when entering Landscape mode, I tried it on my other computer landscape mode worked fine, however it would not show up in my laptop which it used to work. Basically there is nothing I can work with related to landscape, I didnt seem to find a similar question in the forum, hope someone could help me with that!!! 
do you have that plugin installed, which collapses the individual windows to the side bar (left)? Maybe its due to the plugin.
I dont think that styling is default by UE5. Try to uninstall the plugin and see, if the problem still persists.
Thanks for your reply! Do you know the name of the plugin? However, I only enabled the water and landmass plugin manually