WordPress + Excel glitch?

Hi, my client has been having an issue with adding tables into posts on WordPress. For some reason, when he goes to cut cells from his Excel file and then paste them into WordPress, all of the table formatting goes away and it pastes in as what looks like either a primitive and unevenly spaced table, or as straight text where everything is jumbled together.

When he emails me the Excel file he’s using, and I cut and paste the cells in, it works just fine and pastes in as it should.

What could be causing this? I suspect it’s something on his end to do with his Excel program, but I’m not sure.

I am running a Mac, with OS Ventura 13.1, Excel for Mac 16.77.1, and the latest version of Safari browser.

My client is running Windows 10, he says he’s using the latest Excel and has tried to cut and paste from both Google Chrome and Firefox and has had this same issue with either browser.

The page I need help with: [log in to see the link]