@Ehle - I assume these are what you are referring to:

Have you tried zooming in/out? As noted in the following article, some of the table modification elements will not be visible if the zoom level is too high:

https://help.miro.com/hc/en-us/articles/360011986519-Tables#h_01F0Z52CGY4WW7V8NPTWQRM0WY

You may need to zoom out and make the table bigger, to avoid having to zoom in really far/increasing the zoom level too high.