There has been a problem with dropdown menus in blogs using the Yoko theme on mobile devices. It the past this could be dealt with by using the Jetpack mobile module. This has now no longer available. There was also a rather complicated workaround using widgets and custom CSS.
As of 27 Jan 2021 there is an easy fix, using the Max Mega Menu plugin.
The plugin is quite powerful and has a lot of setting, but using it to fix the Yoko probelm is very simple:
Activate the plugin in Dashboard->Plugins, click Activate under the Plugin name.
Go to the menu section of the dashboard: Appearance->Menus
Load the menu used for Primary Navigation and tick the enable box in the Max Mega Menus’s Setting