You'd have to check your version, but from XLv.X Help
("specifications"):
Feature Maximum limit
Row height 409 points
Since there are 72 points per inch, if you're using the Wintel
standard 96 pixels per inch
409 pt * (96 px/in)/(72 pt/in) = 545.3333333 px
which is probably close enough to 546.
Don't know of any workarounds.
If you're using that much text, you might consider switching to
Word. I know lots of engineers who use XL as a word processor, but
it does have a downside.