1. Merge cells. Select the cells you want to merge, and then click the Merge and Center button on the Formatting toolbar. In this way, when multiple cells are merged into one, only one data can be filled in, and the border will only be displayed in the merged large cell area.

2. Center across columns+format the border. Select the cells to be merged, and then choose menu: to center the text of the first cell in multiple columns. In this case, the cells are not merged and the data position can be flexibly adjusted. You can set the border flexibly according to the adjusted text.

I may not understand your needs thoroughly, but I hope it can help.