Depends on what kind of problems mostly. If you need metrics, Prometheus and its ecosystem is as simple as it gets on or off Kubernetes. There are good quality “packages” for any kind of “infrastructure as code” solutions, like Ansible too.
For logs, there’s Loki which is a lot saner choice than ELK in 2025.
To have proper troubleshooting abilities, you will need a bit more than tooling. You should also need to spend some time instrumenting your apps (Prometheus exporters can only take you to a certain level, e.g. node_exporter for host level stats, or other technology-specific exporters) with metrics, and ensure that your apps are logging in a structured way at least.