Several existing answers on this site offer advice related to this question. One of the problems is that dropdown menus and dropdown selectors just get called "dropdowns", which can make it tricky to find stuff. I've mixed these answers in with a couple of my own suggestions. Links throughout and at the bottom.
Make Sure This is Really a Problem
As with so many issues like this, the primary driver behind the change appears to be your subjective opinion that that this type of selector feels slow.
Research does give us reasons to avoid unnecessary depth in navigation systems, but that doesn't mean that dropdowns are a universally bad choice.
With a robust implementation and a relatively small number of options, a dropdown might work, and you could save yourself a lot time and effort by first testing your hypothesis. You might find that this isn't really a problem at all.
1. Just Show All The Options
Depending on the number of options in your set, it may be viable to just show all the options. Your question included two bullet lists. If you took Group B, moved it up and right, beside Group A, make all the items links, indent sublinks, and have a designer tweak the layout to fit with the style of your page, you've got a usable implementation that's as simple as it gets.
2. Just Use a Dropdown
As mentioned at the top, if your menu is small, a dropdown could work. Just make sure you don't stray too far from conventions and adhere to best practices.
2.a. Dropdown Variation - Drilldown Menu
Drilldown menus bridge the gap between standard dropdown functionality and a more wizard-like behavior.
3. Make it a Mega Menu
Mega menus get the NNGroup's blessing and are recommended as a solution to the usability problems of regular dropdowns. They provide a way of reducing the depth in a menu, but can become unwieldy if overloaded.
Applied to your case and example data, if a user clicked on the Group A link, they'd see a panel that shows all the workflows under Group A, including the third level items A1.1 and A2.2
4. Filter More, Navigate Less
This falls into the category of 'Show everything and let the user filter out'. It may not be a appropriate given the number and type of items you, but I've included it here to provide food for thought and potential inspiration
There are lots of options to explore for filtering on menus, one, for reference, is Live Filtering.