It’s been a while since I used a WordPress.com theme on a self-hosted site.
The way it used to work is that some themes (not all themes) were available to download from WordPress.com. So you would download the theme and then you would upload it to your self-hosted site.
That’s not how it works any more. I found that out when I was looking at the Attar theme.
I didn’t want to use it on any of my existing sites on WordPress.com but I saw it was available for download.
So I downloaded it and then uploaded it to a one of the spare self-hosted sites I have.
It didn’t work.
A message came up that said that the theme needs ‘blockbase-wpcom’.
I thought blockbase must be a parent theme, so I looked for it in WordPress.com site directory, but I couldn’t find it.
So I asked Support.
From that I learned that the way to use any WordPress.com theme on a self-hosted site has changed.
All themes that are WP.com themes require a Jetpack connection so they can be used on self-hosted WordPress sites.
Jetpack acts as the link.
So the way to do it is to install the Jetpack plugin on the self-hosted site, and connect it to your WordPress.com account. Then, in your WordPress.com account admin, under ‘My Sites’, choose the self-hosted site and activate the theme (Attar in this case) from there.
I wonder what happen if the link breaks – such as for example if one were to deactivate Jetpack. Would the site break? I guess it would.
Update 17 May 2022
Look at the comments here and you will see that Jen T of WPcomMaven pointed out that the blockbase theme is available of download.
I had missed it because I had looked for block-base.
So I downloaded blockbase from WP.com and then uploaded it, and activated Attar. And it was broken. That lead me to think that what WordPress Support had said might be true – that it needed a Jetpack connection.
So I connected Jetpack and still the error persisted. So I reported it and…. Support confirmed I had found a bug in the Attar theme.
This is the comment line that describes the problem
// updater for WordPress.com themes if ( is_admin() ) include dirname( __FILE__ ) . '/inc/updater.php'; So now I still don’t know whether Jetpack is needed to get the Attar theme to work.
Watch this space.
Photograph Works 
Curious, blockbase can be downloaded here https://wordpress.com/theme/blockbase
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Thank you. Of course! I looked for block-base. I am going to try it with the self-hosted site.
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See the Update in the post.
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Did you install jetpack first or only later? Inquiring minds and all that.
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I tried it without Jetpack first. I was thinking,’Huh! Blockbase is available and I bet Jetpack isn’t needed’.
When that didn’t work I tried the ‘Jetpack way’, thinking it was the essential missing link.
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Hi, I’ve tried to download the theme “Appleton” and facing the same problem you had. I think it can be fixed by changing the parent theme from “blockbase” to “appleton-wpcom” then it looks like it is working, with no errors.
https://wordpress.com/theme/appleton
https://en-gb.wordpress.org/themes/blockbase/
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Hi, I’ve tried to download this theme “https://wordpress.com/theme/appleton” and facing the same problem you had, missing the parent theme, “appleton-wpcom”.
Then I downloaded this theme “https://en-gb.wordpress.org/themes/blockbase/”, unzipped it and changed the folder name to “appleton-wpcom”. It looks like the error is gone.
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Thanks – If I get the energy to get back into the fray I will try it.
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