I know it is possible to create new company (tenant) in SAP Business One Cloud unattended way (using SLD API),
But I did not find any working solution for On-Premise version.
Anyone know any method that can be automated besides this manual process (WinAppDriver)?

I totally get where you're coming from. Automating tasks in SAP B1 can be a lil tricky, especially when it comes to On-Premise. I would suggest :
B1WS (SAP Business One Web Services): you should try explore B1WS, might help. It's a web service interface for SAP B1 and might have the capabilities you need for creating companies.
Custom Scripting: could be a lil complex tbh, but this depends on your specific requirements, you can write custom scripts that interact with SAP B1's database directly.
Third-party Automation Tools: I only know these tools you can find alot more if you will use this method / solution (https://stackoverflow.com/a/50251561/10216101). They're not the most elegant, but they can help you automate the UI-based process in SAP B1 On-Premise.