How do you stop the character being included in region3's?

-- EDIT --

A way you can make your code ignore the character is by using the ignoreDescendentsInstance argument of the FindPartsInRegion3 function. This argument should be an instance, every descendant(everything in it) will be ignored from the returned table but will still count torwards the maxParts argument. So, your code SHOULD work but since for some odd reason it isn't then i'm going to suggest an alternative;

There is no real way to whitelist a Region3 range table effectively without the development of a custom Region3 system.. so an alternative for you is while you're iterating through the partsInRange table, you can check if the current index's parent is equal to the character. If it isn't then add Velocity, if it is then don't.

But just doing that won't stop hats or tools from gaining velocity.. so how about we add another conditional to check if the part's Name is Handle

local player = game.Players.LocalPlayer
local char = player.Character

local region3  = Region3.new(
        Vector3.new(char.Torso.Position.X -20, char.Torso.Position.Y-5, char.Torso.Position.Z -20), 
        Vector3.new(char.Torso.Position.X+20, char.Torso.Position.Y+10, char.Torso.Position.Z +20)
    )

local partsInRange = game.Workspace:findPartsInRegion3(region3, char, 20)

for _, part in pairs(partsInRange) do
	if part.Parent ~= char and part.Name ~= 'Handle' then --Check
		local dist = (part.Position - char.Torso.Position).magnitude
		part.Velocity =  char.Torso.CFrame.lookVector * dist
	end
end

--EDIT--

Another way you could do this is by using the IsDescendantOf function for the checking while iterating through the table..

for _, part in pairs(partsInRange) do
	if not part:IsDescendatOf(char) then
		local dist = (part.Position - char.Torso.Position).magnitude
		part.Velocity =  char.Torso.CFrame.lookVector * dist
	end
end

--EDIT--

And finally, there's another option.. you could look into the FindPartsInRegion3WithIgnoreList function. More info here.

Sorry for all the edits, i'm just researching some stuff and editing when I come across something else that could help you solve your problem.