Documents inherit their styles from the template at the point of creation. From that point forward the styles in the document are independent of those in the template unless changes are explicitly saved back to the template. The only exception to this is if the document is set to automatically update styles.

The template "normal.dotm" is personal to the user so nobody else will be opening your template. Share the document with anyone else though and they can certainly mess with the formatting, but only in the document.

If the test document is based on the template you created then you have not set the template up correctly. The default font for the document is shown as Times New Roman.
Screenshot 2025-04-17 141210.png

For table styles to work correctly it is essential that they are inserted in a paragraph formatted with a style that matches the document defaults. For details see BEHIND THE CURTAIN: STYLES’ ORDER OF OPERATIONS and BEHIND THE CURTAIN: STYLES, DOC DEFAULTS, STYLE SETS, AND THEMES

The default table style used is Table Grid which is set to use Calibri 11pt, which is likely where the 11 point text is coming from. Calibri is also the font for the theme that is attached to the document/template.
Screenshot 2025-04-17 141156.png

If you want your documents to be consistent then you first need to ensure that your template is consistent. Based on the document you posted your template needs work.