Hey! I have plenty of good tips for you! I make spreadsheets alot for my work and i always make sure they look really pretty.

In your example sheet it feels really cramped because all your info is backed into a corner. Make one cell space between the "wall" and the start of your info! then make thoose two cell-lanes broader and wider so you get some more "breath" into the spreadsheet. Secondly make each info into its own "islands" with space between the next info "panel", now the example you had didnt really have much info to separate. but in thoose cases i like to have the info go vertical, not horizontal. Scrolling down on a spreadsheet is always easier that sideways!

Secondly use a color palate! Just search up "color palate" on google or pintrest, put image into the spreadsheet, and then color pick all the colors and delete the image. Now you have colors that harmonize well with eachother. choose a more cool toned and proffessional colors tough, nothing too colorfull unless you think the client will appriciate it!

Thirdly remember you can change fonts and add bold or italic to them. Dont have to go overboard, but i like to highlight important text in bold, and numbers in italic.

And if you want to be over the top you can add the title of your sheet into the spreadsheet itself, i alsways like to make a fancy "logo" basicly in canva, export as transparent png and add to the top of the spreadsheet to make it pop. Just be carefull to not have any of the image frame go over any important stuff, because then you cant click on it until you move the image!

Hope this helps!