Excel online - formatting changes when copy-pasting, paste options not available

I borrowed my sister’s macbook to edit some files. She doesn’t have excel installed so I’m using excel online.

I’m mostly copy-pasting stuff from the original file to the new form that was given to us. It was working fine at first until I changed the local format from English (US) to English (UK) because the dates format had to be changed from mm/dd/yyyy to dd/mm/yyyy which seemed unavailable on English (US). I’m not sure if the change in local format is what’s causing this but now, everytime I’m trying to paste stuff to the new file, it’s not keeping the proper format so I thought I’ll use the paste option to keep the format but the paste options are not available now.

I already searched on google and it said to go to file>options>advanced but as you can see on the photo there is no”advanced” option anywhere.

Please help, thank you very much!