In this documentation, we can check how to use iframe in Joomla.
1) Login to Joomla admin panel.
2) Go to ‘Extensions’.
3) Click the option ‘Plugin’.
4) In the ‘Filter’ section, click ‘Select Type’ and then click ‘Editors’.
5) Click on the option ‘Editor-TinyMCE’.
6) Find out the section ‘Prohibited Elements’ and remove ‘iframe’ from it.
7) Click the button ‘Save’.
That is how we can use iframe in Joomla.
If you need any further help please reach our support department.