Bit of incorrect information going on in this page so doing some work to steer people correctly here and then provide solution to OP's problem;
SendKeys are only utilised by the following attributes as of v6.4
UI Elements:
Button (UIA) elements
Check Box (UIA) elements
Radio Button (UIA) elements
Combo Box (UIA) elements
Edit Box (UIA) elements
Menu (UIA) elements
Menu Item (UIA) elements
List (UIA) elements
List Item (UIA) elements
Table (UIA) elements
Tab Control (UIA) elements
Tab Item (UIA) elements
Hyperlink (UIA) elements
Tree View (UIA) elements
Tree View Item (UIA) elements
Window (UIA) elements
Active Accessibility Elements:
Button (AA) elements
Combo Box (AA) elements
List Box (AA) elements
Edit (AA) elements
And lastly
Application elements (what some people call the root element)
SAP Main Windows
These are the only places you can use Send Keys.
As for Send Key events, these are for utilizing send keys typically on thin client applications like Citrix. A great explanation is posted here:
https://www.rpaforum.net/threads/global-send-keys-and-send-key-events.1587/
Also there is a data sheet on Send Keys called 'Guide to Send Keys and Send Key Events on the Blue Prism portal would recommend you read it. For the purposes of answering here to Op's various questions.
If you spy with HTML mode you can't use a HTML element to invoke Send Keys. You can use the root application sure but not the actual spied element. There is a sequence of events you could try where you use HTML/AA/similar to click the element you are targeting and then afterwards utilise either an element listed above or the root element to invoke send keys to perform the task you are looking for. In this case teh task you are trying to do in send keys is
{DOWN}
for the down arrow or
{PGDN}
for page down if you wanted instead and then
{ENTER}
for the enter function
As stated by Blue Prism and other resources unless you absolutely need to do not use Send Key Events, it is not preferred.