Word Tables Support formula calculations, so after you insert a table in the WordNote, you can insert formulas into the cells.

You can perform calculations and logical comparisons in a table by using formulas.

The Formula command is found on the Table Tools, Layout tab, in the Data group.

Merged cells are not supported in OneNote's native tables.
And WordNote is a Word-based plugin note.
The Word table itself supports merging cells. So, merging cells is also natural supported in WordNote.