The great writers? They all have betas. Are you interested in using a beta for your work? Not sure where to find them? Goodreads has groups. Join a group that you like. For example, I joined M/M Romance. They have resources for writers who love to write about men who love men. Well, included in that is a link where you can find betas and authors who need them.
Are you a reader interested in being a beta? Well, that could work for you. Are you an author who needs a beta (because if you're an author, you really need a beta), then it might work for you.
No matter what you do, get a beta.
The other issue? How much to give them. Well, I started out with half a book. Then, I asked a friend and went chapter by chapter. The problem with that for me has been consistency. The plot holes? They are many if your beta doesn't get the book to read so the book can be read with fluidity. They can't know what they're missing if they're missing most of the book. So, I'm moving back to the whole book.
Sometimes with a few tears along the way.
Hope you're having a great week.