Works for me

With the current GPGME master and the forthcoming T4551 release this has been fixed.

I did encrypt the file myself with the version mentioned above.

I see the regression of gpgconf. I wonder if it's better to fix gpgconf side, too.

I see a regression with your fix. This option is even controllable with gpgconf at the basic level. It would be better to make it a dummy option.

Fixed in master. Closing.

Fixed in master (to be 2.3).

I tried to apply&push, since we changed the file a bit, I needed to apply it manually.
Anyway, it's done.
Closing.

I meant, 'card-timeout' was not intended for controlling caching PIN on card. It was for "DISCONNECT" command support.
I'm going to remove questionable documentation.
Closing.

No worries -- you led me in the direction of a solution when you mentioned loopback mode. I appreciate your time and your help!

While it's not recommended, current master has a support of sharing same raw key materials. I think that it now works (I don't try, though).
Closing.

Thank you for your fix suggestion. I think your change is good. I applied and pushed.

Sorry, I responded in a mode of "tracking a bug to fix soonish". I should have changed my mode into showing HOWTO.
Thanks for sharing useful link.

I found these instructions for pinentry loopback in Emacs, and they worked!

When you can configure it properly, there is a way to workaround it.

A newline is required by the PEM standard.

Maybe the file was encrypted with a version of gpg4win-3.1.5? We had a serious bug there that sometimes files were corrupted. See: T4332

Thanks for taking this one.

This is problem of your setup of your build environment. Closing.

We got reports from Ubuntu users, perhaps, it's good to refer:

I added the section in tools.texi. Closing.

For (1): it is broken out-of-the-box, that would be true. When you can configure it properly, there is a way to workaround it. Well, I admit, it's not yet perfect.

Thank you for that analysis. I don't understand some of the parts (because I don't know anything about pinentry), but I do have some questions.