in WordPress 5.0.2 the ARVE button, (for adding the shortcode into the text edidor), has been dissapeared. How can add an ARVE video now?
I guess you mean the new Gutenberg Editor that came with 5.0+. There is currently no button because the Shortcode UI plugin used for that is not comfortable with Gutenberg. You have to manually write the shortcodes with the shortcode block, its pretty easy and the docs help you. Or just use the embed block that not uses shortcodes but also has no options and will just ARVE defaults as set on settings page.
You can also install the classic editor plugin to continue use the old editor and the ARVE button will be there.
I plan to add a ARVE Gutenberg block in the future.