In administration overview i can see these warnings:
MySQL is used as database but does not support 4-byte characters. To be able to handle 4-byte characters (like emojis) without issues in filenames or comments for example it is recommended to enable the 4-byte support in MySQL. For further details read the documentation page about this.
Your web server is not properly set up to resolve “/.well-known/caldav”. Further information can be found in the documentation.
Your web server is not properly set up to resolve “/.well-known/carddav”. Further information can be found in the documentation.