Issues with the gallery

Hello there,
i have issues with the gallery in the new Gutenberg editor.

First:
Where do i find the option, to sort the images randomly?

Second:
How can i get the gallery to use the old css classes and elements like it did before Gutenberg? My old postings are all fine, but the newly created ones are not of the style of the old ones:

Old one: https://www.spielmannszug-meschede.de/2017/10/neuer-aussenanstrich-fuer-die-huette/

New one: https://www.spielmannszug-meschede.de/?p=2947&preview=1&_ppp=9c6a10acbc

There are completly different classes and elements used to build the gallery. Now my theme does not handle them and i have to repair the theme. I did not saw these differences than i checked the new version before the update. How do i get the old css-classes and html elements back without manually editing the code in the posting?

Could you please help me to get the new gallery back to look like the old ones?