The welcome text can be edited with HTML-tags.
To adjust the default text, go to > Settings > General > System > "Show this text on the login page" and edit this text as wished, for example:
<center>
Welcome to the login page of<br>
<b>virtual assembly<br>
of the Happiness association</b><br>
login will be possibly from 21st April 2022 at 12:45<br>
In case of technical difficulties please contact<br>
[Support-Contact - mail or phone]
</center>
You can also embed images:
<img src="https://[YourInstance].openslides.com/media/[YourImage.png]" alt="[AlternativeText]" width="280" height="57" /><br>
The link to the image (https://[YourInstance].openslides.com/media/[YourImage.png]) must be freely accessibly from the web.