bootstrap 5 – load dynamic content into modal/offcanvas – pure vaniall js and ajax – no jquery

how can I load dynamic content into a Bootstrap 5 Modal.
With pure vanilla js (no jquery!).

I have e.g. the index.php.
I want to open a modal with a button.
The button should pass a URL (e.g. /example.php)

Then the modal should open an load the example.php into the modal body.

Can you help me with this?
Thank you so much!

I only found old or jquery solutions. But I don’t want to use jquery with Bootstrap 5.