This is weird!  I tested the update on our DEV server ( clone of our live server) and it updated 100% fine to 2.11
Joomla 3.10.11 on PHP 8.0.27

BUT, when I then went to update on our LIVE server, I got this error:

An error has occurred.
-1 Copy file failed

I can't find any trace of this in PHP error logs, or Joomla  
Any hints about where i might be able to see what files are failing and where permissions are out. ???
(Actually they should not be any different than the permissions on our DEV server, where the update worked...)

after the failed update, the K2 blogs all work fine in front end and back, unless i click on a link to the category.. then I get this:

 Error: 1176 - Key 'idx_item' doesn't exist in table 'i'

ouch!!

I'm not sure we are ready to switch to PHP8.1 yet!

I just updated our DEV server with a refresh from our Live server, and now it crashes updating on DEV :(
(from 2.10.3 to latest offered 2.11.20230112)

"An error has occurred. -1 Copy file failed".

Downloaded "reinstall" and get the same error

"An error has occurred. -1 Copy file failed".

Permissions issue?? I have no problem updating any other Joomla extension, ( and I used to be able to update K2 just fine) Not sure exactly what needs to be re-set

this is what the debugger shows

RuntimeException [500]
Copy file failed
.../libraries/src/Filesystem/:160
155 }
156 else
157 {
158 if ([email protected]($sfid, $dfid))
159 {
160 throw new \RuntimeException('Copy file failed', -1);
161 }
162 }
163 break;
164 }
165 }

bottom of stack:

Joomla\CMS\Application\CMSApplication->execute()
.../administrator/:51
46
47 // Instantiate the application.
48 $app = JFactory::getApplication('administrator');
49
50 // Execute the application.
51 $app->execute();

top of stack:

Joomla\CMS\Filesystem\Folder::copy()
.../libraries/src/Filesystem/:134
129 switch (filetype($sfid))
130 {
131 case 'dir':
132 if ($file != '.' && $file != '..')
133 {
134 $ret = self::copy($sfid, $dfid, null, $force, $useStreams);
135
136 if ($ret !== true)
137 {
138 return $ret;
139 }
Arguments
src
string(128) "/var/www/html/sitename/html/tmp/install_63e7fb4ae3e3d/k2-master/media/k2/assets/vendors/verot/"
dest
string(92) "/var/www/html/sitename/html/media/k2/assets/vendors/verot/"
path
NULL
force
bool TRUE
useStreams
bool FALSE

update: i found the problem, I HAD FORGOTTEN that back in November when we changed to PHP8 I had edited the ancient php file in
/var/www/html/sitename/html/media/k2/assets/vendors/verot/class.upload.php/src to fix a PHP8 error... and apache lost ownership ( oops)

FIXED with corrected apache:apache permissions - Update went through just fine.

All working fine now, sorry to bother you!