Allow nextcloud.log at upgrade

Is it an idea that nextcloud.log is accepted as file when Nextlcoud is upgraded?

What do you mean? Can you reword your question and/or provide more context?

When I start the update from the online updater, I got a message that nextcloud.log is an unaccepted file. Then the update stops.
After I removed the file, the update works perfect.

The locations the Updater checks for unexpected files should not contain your nextcloud.log unless you’ve configured something strangely.

What is your logfile parameter set to? A typical value would be the path to your data directory + nextcloud.log. In fact that’s the default unless you override it.