I need help with Minecraft?

I need help. As read in the title is about Minecraft. I'm building a cinema and have a Texurpack in it. Is there a way for the Bedrock Edition to build a milk (popcorn) and mushroom soup (nachos) farm without mods. Also with link.

Mushroom Farm goes:

or "milking" a mushroom cow

And milk farm too:

just milk a cow

But how do I manage that the cows do not disappear. I have already tried it with leash and they are nevertheless despwant.

You have to give them a nametag, then they will not despaw

Thanks