Still working just fine here with WordPress 5.1.1.
Did you install the Classic Editor plugin? You need that to retain the original WordPress editor after they switched to the visual/blocks Gutenberg editor in WP 5+. I have NOT added anything to my plugin to add “blocks” to that Gutenberg editor, so you still have to use the shortcodes.
Classic Editor plugin (a must is you hate the Gutenberg editor as much as everyone else does):
https://wordpress.org/plugins/classic-editor/
Also, the shortcodes are listed on the documentation page with all the possible arguments, so you really only need to copy and paste and change things the way you want the first time you set up your sheets display. After that, the shortcodes plugin isn’t really needed unless you need to change that on a regular basis for some reason.
Documentation:
https://stephensherrardplugins.com/docs/pta-volunteer-sign-up-sheets-documentation/