Yield Tech is a feature that helps to prevent your visitors from feeling overwhelmed as they view your site. When you toggle on this feature, it prioritizes which Form displays and prevents the others from loading.
You can find this feature in List Builder, in the Visibility tab under the Advanced Settings section for these two Form Types: Popups and Scroll Boxes.
Despite the other Form Types not having this feature displayed under their Advanced Settings section, they do play into the overall flow of Yield Tech when it's turned on for Popups, Scroll Boxes, or both Form Types.
Welcome Mat: When the Yield Tech feature is turned on for either Popups or Scroll Boxes in List Builder and a Welcome Mat is live, the Welcome Mat always loads first and takes up the whole screen. This blocks any other List Builder Forms from loading.
Popups and Scroll Boxes: If there are no live Welcome Mats, and if a Popup and a Scroll Box are both set to be live on the site, then whichever one loads first is the one that's displayed. For instance, if a Scroll Box happens to load first at load time, then the Popup doesn't display. If a Popup loads first, then that blocks the Scroll Box from displaying.
Additionally, if you have multiples of Popups set to load on the same page, each has an equal chance to be displayed when the page loads. The same goes for Scroll Boxes.
Other Form Types: Smart Bars, Inline Forms, and Click Triggers are not going to be affected at all by the Yield Tech flow. These will show regardless of whether Yield Tech is turned on. As mentioned above, Welcome Mats using the Embedded Display Mode will similarly be unaffected.