You can use the website variable to check if the invoice report is printed from the website

website
the current website object, if any (this item can be present but None)

Try the following code:

<t t-if="website">
    <div class="from_website" >
        <strong> Printed From Website</strong>
    </div>
</t>

Edit (Report Preview)

You can add an extra parameter to the report URL (inside the report_pdf_preview.js file ?variable_name=) and alter the _render_template function to add a new report value based on the URL parameter then use it inside the template to hide text if the user uses the report preview.

Example:

class IrActionsReport(models.Model):
    _inherit = 'ir.actions.report'
    
    def _render_template(self, template, values=None):
        values['pdf_preview'] = request.params.get('pdf_preview')
        return super(IrActionsReport, self)._render_template(template, values=values)

You can hide an element like following:

<div t-if="not pdf_preview and website">
  From website
</div>