Drupal 8.x

I can do this easily my d7 site, but on my d8 site their no "has taxonomy terms" in the filter criteria of the views. How do I add it there?

What is the best and straightforward theme to use for building a site?

I tried starting with Bartik, but then I noticed Bartik doesn't use node.html.twig to display nodes, which I don't understand.

So what would be a straightforward but full-featured core-like theme to use when building a site, and that keeps getting updated with every new Drupal Core version, but at the same time doesn't use additional modules and components ?

How can I upgrade to drupal9?
Also, do you have auto-update?

Has anyone else had difficulty in making the PayPal button html code work in a D8 block?  I had no trouble with my D7 site and even tried copying that functioning code over, but all attempts simply display the code as text.  YES, I've set format to FULL HTML... below is the code I am using:

Hi all. I'm completely new to Drupal.

I have just installed 8.8.5 using Softaculous on a really cheap budget shared hosting account. 

The site works and I can access the admin area fine.

When I try to install a 50kb module by uploading or URL I get a blank page this error message "The website encountered an unexpected error. Please try again later."

My first thought is upload size, but as it's only 50kb I doubt that's the problem.

My next thought is permissions. Do I need to change any folder permissions to allow the upload?