Breadcrumb separators! By default, you get a ":" (colon) after the "Home" breadcrumb and then a forward slash "/" for subsequent breadcrumb separators. While changing the Home breadcrumb separator can be performed in the RoboHelp GUI, changing the subsequent breadcrumb separators isn't so obvious. But I'm still learning the new GUI so maybe there's another/better way to do this, in which case hopefully someone can reply with it. If not, the method here worked for me, and I logged a feature request to have this config functionality added to the RH 2019 GUI for frameless output.
Change the home separator
Go to Output>Labels>English (US) (this is the default/only language for my project - yours may be different) and select FRAMELESS. In BreadcrumbStart, replace the ":" character with the "|" - or whatever character you prefer. Save the changes. That's the easy one. The forward slash is a little trickier.
Change subsequent separators
Finding where to change this took some digging, but it appears to be controlled/specified using the following code in several instances of the layout.css file that are installed/stored under the RoboHelp 2019 program files (file paths provided below):
Tip: Before making these changes, shut down RoboHelp, create backup copies of each layout.css file (e.g., copy and rename to layout.css.original). You may also need to blow out your output files before generating the output to view the changes (I'm not sure yet if generating output completely overwrites every existing file in the output location or just those it detects have changed).
Logged a feature request with the RoboHelp dev team to incorporate this configuration functionality into the RH 2019 GUI.