I'm a LibreOffice user who recently had to use Excel. Most things I was able to figure out, but two things really stood out as problematic with Excel.

First, the keyboard shortcuts have no mnemonic. It's just random letters. No way to actually remember them.

Second, there was no way to have the row and column of the current cell highlighted. This made it difficult to find where I was - very important not to screw that up on a PCBA BOM.

I've not found any objective UI problem with LibreOffice Calc. It's not perfect, but it is intuitive and feels like the people who wrote it, use it.