The mask and pen tools under opacity in the Effects Control panel are missing.

​@FeliciaVG With Premiere version 26.0, we’ve reworked the masking tools. You can now find them in the Tool palette (the little thin panel with the selection tool, razor blade, etc). Click and hold on the Object Mask tool and you’ll see the options for circle, rectangle, and pen masking tools.

In this new workflow, you start by selecting the clip in the timeline, then choosing one of the new masking tools, then drawn your shape. The mask will appear in the Effects Control Panel and can be dragged on to any effect to mask the effect.

More: https://helpx.adobe.com/premiere/desktop/add-video-effects/work-with-masks/rectangle-ellipse-and-pen-masks.html

More about the new Object Masking: https://helpx.adobe.com/premiere/desktop/add-video-effects/work-with-masks/object-masking.html