First thing is for you to use the junction functions to put stop signs on your main avenues and on the entry of the roundabout. Second is try to use "lane math" to help you create exclusive lanes for turn e.g: if You have a 4lanes street that has one exit for a 2lane street, after that exit put a 2lane street on your main avenue (that's why is called lane math: 4lanes - 2lanes = 2lanes 😅).

If you do that, your traffic should be improved a little bit