Cannot embed a Synthesia video that is keyboard accessible

We are using both Synthesia (embedded block) and Rise 360.  With a new requirement for accessibility, we are testing keyboard accessibility by tabbing to each actionable item in the Rise course.  For some reason, the tab skips over the Synthesia video.  It's important to use the embedded video, as there are features in Synthesia that are only available with the Synthesia video player. particularly their closed captioning and interactivity capability.  There is an option in the Tab block to embed a video, but it then opens the video in another tab (which isn't embedding by the way).  We've tried other video streaming tools like Brightcove and it is keyboard accessible.  Not sure why Synthesia isn't.  Has anyone else run into this issue and how to work around?