You can use a web service called Browserling to run web based apps including Whatsapp web. Indians have been using this workaround for their Jiophones which also run on KaiOS. Don't know about any other methods or apps you can get running.
I'm not Indian and never had a phone that used this operating system.
Google "whatsapp jiophone" if you need to find instructions. I cannot garuntee the workaround will work on an unreleased phone.