When upgrading an application to APEX 19.x, if you have a Switch page item it probably still looks like the old "Yes/No" boxes:

{% asset_img old-swtich.png %}

To change to the new, more modern, Switch item you need to change this for the entire application. Do to so go to Shared Components > Component Settings > Switch. From there set the Display Style to Switch. All the Switch items will now look like:

{% asset_img new-switch.png %}

For all new applications created in 19.x the Display Style is already Switch so there is nothing to do in order to have this type of Switch.