Here’s an example:
Step 1: Create an email and write your message as per normal.
Step 2: Open a new Google Sheet (in a separate tab or window).
Step 3: Create your table in the Google Sheet. Format it as you like.
Step 4: Copy all the cells in the table.
Step 5: Return to Gmail and paste the cells into your email message.
As you can see, all the cells and table formatting are maintained. You can add multiple tables using this method.
Note: If you want to include a very large or complex table, it might be better to provide a link to the Google Sheet in the email instead. But for simple and small tables, this method works well!