This is a problem I have only had with Office 2021 since upgrading.
I am trying to create a table but I keep getting random black lines throughout the table. The table is essentially completely white borders (black page color), with various colored cells to enter text on. The black lines appear (mostly) horizontally on top of the white border. Sometimes it is one row, sometimes more. Sometimes I zoom out or in 10% and the lines disappear, but move to different rows or vertically on one side of one cell. Or they will appear randomly as I modify a cell's composition.
As you can imagine, this is incredibly frustrating having had no issues at all with previous versions.