When using the scoreboard command, it wont convert shorthand entity UUID.
By shorthand I mean that you can use something like 0-0-0-0-0 to target an entity with a UUIDMost and UUIDLeast of 0.
But with the /scoreboard command, there is a difference between the shorthand and full UUID.

Steps to reproduce
/scoreboard objectives add posx dummy
/scoreboard objectives setdisplay sidebar posx
/summon minecraft:armor_stand ~ ~ ~

/scoreboard players set @e[type=minecraft:armor_stand,sort=nearest,limit=1] posx 1
/scoreboard players set 0-0-0-0-0 posx 1

You can see that there are 2 different entries on the scoreboard list.
To prove that shorthand works with other commands, you can do similar to
/tp 0-0-0-0-0 ~ ~ ~
/data get entity 0-0-0-0-0
/execute as 0-0-0-0-0 run scoreboard players set @s posx 1

You can still use the full UUID, such as 00000000-0000-0000-0000-000000000000