Something to try using the OP code
local function updatehotkey(self, actionButtonType)
local hotkey = _G[self:GetName() .. 'HotKey']
local text = hotkey:GetText()
text = string.gsub(text, '(s%-)', 'S')
text = string.gsub(text, '(a%-)', 'A')
text = string.gsub(text, '(c%-)', 'C')
text = string.gsub(text, '(Mouse Button )', 'M')
text = string.gsub(text, '(Middle Mouse)', 'M3')
text = string.gsub(text, '(Num Pad )', 'N')
text = string.gsub(text, '(Page Up)', 'PU')
text = string.gsub(text, '(Page Down)', 'PD')
text = string.gsub(text, '(Spacebar)', 'SpB')
text = string.gsub(text, '(Insert)', 'Ins')
text = string.gsub(text, '(Home)', 'Hm')
text = string.gsub(text, '(Y)', '1')
text = string.gsub(text, '(U)', '2')
text = string.gsub(text, '(I)', '3')
text = string.gsub(text, '(O)', '4')
text = string.gsub(text, '(P)', '5')
text = string.gsub(text, '(H)', '6')
text = string.gsub(text, '(J)', '7')
text = string.gsub(text, '(K)', '8')
text = string.gsub(text, '(L)', '9')
text = string.gsub(text, '(B)', '10')
text = string.gsub(text, '(N)', '11')
text = string.gsub(text, '(M)', '12')
hotkey:SetText(text)
end
hooksecurefunc(ActionBarActionButtonMixin, "UpdateHotkeys", updatehotkey)
ActionBarButtonEventsFrame:GetScript("OnEvent")(ActionBarButtonEventsFrame, "UPDATE_BINDINGS")