Yes, there is an Alt key combination to enter the infinity symbol in Excel. Here are the steps:

1. Place your cursor where you want to insert the infinity symbol.
2. Press and hold the Alt key on your keyboard.
3. While holding the Alt key, type the number 236 on the numeric keypad.
4. Release the Alt key.

The infinity symbol (ˆž) should now appear in the cell. If you don't have a numeric keypad on your keyboard, you can also use the Character Map tool in Windows to insert the infinity symbol. Here's how:

1. Open the Character Map tool by searching for it in the Windows Start menu.
2. In the Character Map window, select the font you want to use (e.g. Arial, Times New Roman, etc.).
3. Scroll down until you find the infinity symbol (ˆž) and click on it to select it.
4. Click the "Copy" button to copy the symbol to your clipboard.
5. Go back to Excel and place your cursor where you want to insert the symbol.
6. Press Ctrl+V on your keyboard to paste the symbol into the cell.

That's it! You should now have the infinity symbol in your Excel spreadsheet.