Using a mcfunction to copy a player's name onto an entity (a zombie in this example) as such...

execute as @s run data modify entity @e[type=zombie,limit=1,distance=..6] CustomName set value "{\"text\":\"Zombie \",\"selector\":\"@s\"}"

Names the entity "Zombie " and ignores the selector portion of the string.

I even tried specifying my own <playername> in place of the @s selector, and it still ignores the selector string portion.