Issues connecting gitlab-agent with my Gitlab CE instance

You should try to connect to GRPC directly by using the following configuration:

gitlab_kas['listen_address'] = '0.0.0.0:8150'
gitlab_kas['listen_network'] = 'tcp'
gitlab_kas['listen_websocket'] = false

Then connect with:

helm .... --set config.kasAddress=grpc://<hostname|ip>:8150/

(Mind the trailing slash)