I use Firefox. I haven't seen those arrows in ages. Which is Okay by me. There may be a setting in Firefox I could change?
Personally, I find the arrows obnoxious to view. As I rarely need the feature.
I checked Chrome and Microsoft's edge browser.
The arrows appear in those browsers.
Browser updates break down-arrow scrolling all the time.
You just demonstrated Software Focus's tutorials are flawed. I don’t care for them or watch them myself.
There is a setting you can change in Firefox. https://support.techsmith.com/hc/en-us/articles/115001901372-Snagit-Windows-Scrolling-Not-Working-in-Firefox
Here’s me looking at a very large image in Firefox.