/appinfo/app.php is deprecated, use \OCP\AppFramework\Bootstrap\IBootstrap on the application class instead.
I just have this spamming on my Nextcloud logs regarding to keeweb app:

Thanks in advance :)
Yes I am aware of this. This is a duplicate of #195 and will be fixed with one of the next updates.
These messages will only be generated as debug messages. So if you disable "debug" in the log, these messages should not appear any longer.
To be more specific:
In config/config.php of your Nextcloud installation make sure that the loglevel is set to 2 - level 0 or 1 should not be used for regular use:
'loglevel' => 2,
Also see https://docs.nextcloud.com/server/latest/admin_manual/configuration_server/logging_configuration.html.
Quote:
By default the log level is set to 2 (WARN). Use DEBUG when you have a problem to diagnose, and then reset your log level to a less-verbose level as DEBUG outputs a lot of information, and can affect your server performance.