Customizations in Classic Editor in Wordpress could be done by "Advanced TinyMCE Configuration" plugin.
Classic Editor in Wordpress is based on TinyMCE editor. Wordpress instructs it how to act, how to look as UI.
"Advanced TinyMCE Configuration" changes TinyMCE startup configuration.
To be able to configure Classic Editor you would need to know know to configure TinyMCE.
Here are some links from TinyMCE documentation:
You could see that DreamsTime offer a week of free trial.
Short answer it NO – in almost all cases you could take no benefits from the free period.
For your free period you receive images with watermarks only.
In fact they cannot be used for almost nothing, not (only) because of watermarks but because of legal restrictions:
ERROR: The login must contain only alphanumeric characters.
If you experience this error while you want to create DreamsTime account, we have solution for you.
If you experience this error with Chrome browser, try different browser, e.g. Microsoft Edge.
That's all.
Its just a bug in software and we hope DreamsTime will fix it soon.