How to morph into any mob Minecraft Java no mods/datapacks

Commands:
/gamerule commandBlockOutput false
/effect give (your player username) minecraft:invisibility infinite 0 true
Put this into a Repeating Command Block with Always Active set to true:
/tp @e[type=(the choice of mob),name=(whatever you named the mob)] (your player username)
Optional Command:
/attribute (your player username) minecraft:scale base set (choose size)

[KimiTNB]

Here is some more important information:
*Commands:
/gamerule commandBlockOutput false
/effect give (your player username) minecraft:invisibility infinite 0 true
Put this into a Repeating Command Block with Always Active set to true:
/tp @e[type=(the choice of mob), name=(whatever you named the mob)] (your player username)
*Some mobs like Striders and Axolotls have unique effects like Fire Resistance and Water Breathing, so if you want those effects, then you will simply have to give the effect to yourself using commands
*You can also use this command to make yourself smaller or bigger so you can be a similar size to mobs like Cod and Sniffers: /attribute (your player username) minecraft:scale base set (choose size)