@NolanDeveloper thanks I have corrected the omission to mention it is only WHILE scrolling

It still opens the menu even if I scroll

@NolanDeveloper You are correct
That comment is less than clear the actual function is HOLD alt without release then scroll !! so have added that too

I'm probably missing something obvious. Behavior for me is such: I hold alt, scroll (it scrolls faster), release alt, menu opens.

@NolanDeveloper Hmm as said different users hardware setting different behaviours (I am using pre-release on Windows 10)
so perhaps your version or windows is adding some extra press or sticky keys ,since for me:
Alt menu function needs 2 "alts" to kick in after scroll as normal function Windows Menu Systems trigger which is "global"(normally will only need one alt).

my best suggestion is find an app that is app aware such as AutoHotKey or a mouse controller like "Highresolution Enterprises" X-mouse (Providing up to 10 layers of button mapping for every profile, Per-Profile Based Scrolling), however messing with mouse scroll is not easy, as driven by different hardware drivers Mouse/Touch screen/Touch pad/JoyStick/Eye tracker etc.. Hence my preference is Auto scroll

To make the changes done by the Registry tweak take effect, you need to sign out and sign in to your user account.

don't think that's avoidable, but see below
https://duckduckgo.com/?q=mouse+scroll+registry+reg&ia=web
Computer\HKEY_CURRENT_USER\Control Panel\Mouse

So not that simple as its a hardware setting at startup so scripting user control panel run time settings is easier
however see https://stackoverflow.com/questions/17040534/how-to-change-mouse-scroll-speed-using-batch-file-in-windows

@NolanDeveloper
I am not the developer but AFAIK the issue is "different windows (users) different strokes"
SumatraPDF is a wrapper around MuPDF and Windows Hardware is a Wrapper around SumatraPDF UX
so SumatraPDF can try to control the speed of MuPDF renders
but it is Windows controls the speed of SumatraPDF and thus may differ from mouse to mouse etc.

As an example the Microsoft brand mouse I am using now will one scroll click jump this page this much at a time at 100% in edge
and at 200% only this much

which is the same as one click at 100% in SumatraPDF Thus Sumatra PDF is 2 times as many clicks as Edge and many complaints that is not slow enough. but with acceleration one click rolls this much

so is considerably faster

@GitHubRulesOK From my experience the scroll behavior of SumatraPDF differs significantly from other windows applications. I have used SumatraPDF in various configurations over the years, on different computers and with different mice, and the scrolling has consistently been noticeably slower than in other applications. The question is whether this is a general issue rather than an isolated case. The specific implementation details of SumatraPDF are not relevant to determining whether the issue exists.