In the past I often updated JCEpro without problems. But now I get an error message:
Warning
Install path does not exist.
Package Update: There was an error installing an extension: com_jce.zip
Before updating ensure that the update is compatible with your Joomla! installation.
You are strongly advised to make a backup of your site's files and database before you start updating.
Error
Error updating package.

Joomla 3.10.12
JCEpro 2.9.38 tying to update to 2.9.41 or 2.9.50 gives this error.

I did what you suggested. But now I get these messages:

Warning
Copy failed: [ROOT][TMP]/install_652ff1dccfcef/packages/install_652ff1dfc6383/jce.xml to [ROOT]/plugins/installer/jce/jce.xml
JInstaller: :Install: Failed to copy file [ROOT][TMP]/install_652ff1dccfcef/packages/install_652ff1dfc6383/jce.xml to [ROOT]/plugins/installer/jce/jce.xml
Plugin Install: Could not copy setup file.
Package Install: There was an error installing an extension: plg_installer_jce.zip
Error
Error installing package

I deleted the first seven folders. The last three didn't exist.
After Installation of new JCEPro version I get this error message:

Warning
Copy failed: [ROOT][TMP]/install_652ffa411f386/packages/install_652ffa44496b7/jce.xml to [ROOT]/plugins/installer/jce/jce.xml
JInstaller: :Install: Failed to copy file [ROOT][TMP]/install_652ffa411f386/packages/install_652ffa44496b7/jce.xml to [ROOT]/plugins/installer/jce/jce.xml
Plugin Install: Could not copy setup file.
Package Install: There was an error installing an extension: plg_installer_jce.zip
Error
Error installing package

FTP show me, that these folders were freshly created:

administrator/components/com_jce
components/com_jce
media/com_jce
plugins/content/jce
plugins/editors/jce
plugins/extension/jce
plugins/fields/mediajce

but thes folders are missing:
plugins/installer/jce
plugins/quickicon/jce
plugins/system/jce