Is it compulsory to take backup before updating ios 18 beta to my iphone 13 ?

We cannot discuss issues regarding any beta version of any Apple operating system in these forums. But offering generic advice, it's always a very good idea to make a backup of any device before updating or upgrading its operating system.

Regards.

As always, you never need to back up any data as long as you don't care if it is lost. For those that fear losing data, you should always have a backup. Actually it has long been recommended to use the 3-2-1 backup method and have 3 backups, 2 on different media formats, and 1 stored offsite.