How do I mount a entity using the data command?

I tried data modify entity @s Passengers append value {id:"minecraft:marker",Tags:["youdied.collector"]} but it won't work. Then I tried summon marker ~ ~ ~ {Tags:["youdied.collector"]} ride @e[type=minecraft:marker,tag=youdied.collector,sort=nearest,limit=1] mount @s this works but after that I can't modifiy the data element of the marker. I tried execute as @s run data modify entity @s Passengers[0].data.player set from storage youdied:main PlayerData it doesn't work. The PlayerData is working because I use it a line below at this command data modify entity @s Brain.memories."minecraft:liked_player".value set from storage youdied:main PlayerData.UUID