Hello @Kos_Kot, welcome back 
Nextcloud version you are using is highly outdated, I would recommend start with supported one either nc30 or nc31 (nc32 planned for end of Sep). Many good examples exist starting from official Docker .examples over more advanced docker-compose-setup-with-notify-push-2024 to custom variants for details use search.
this is the foundation of the system - start troubleshooting here - review logs 101: logging, which logs exist, how to access and understand, DNS, routing, firewall. return with more details if you need help. I feel 101: Self-hosting information for beginners could help you for better start. Once ready look at Collabora integration guide - similar to OnlyOffice but more common and IMO the way to go today.