Combine SharePoint with a structured hierarchy for processes (sites, hub-sites)

Dear Community

Currently I am looking for approaches to a solution to create a process management solution based on SharePoint Online.

The solution should cover the following requirements:

• A kind of hierarchy should be built, which should represent main processes and sub-processes.
• Subprocesses can contain lists or single documents
• A main process can contain no, one or more subprocesses
• Subprocesses can again contain subprocesses
• Permissions must be assigned at the level of main processes and subprocesses

Current approach:

The top level is a sharepoint hub site. Various sites are attached to the hub site, which are used as main process or sub process. Now the linking of the individual processes is more difficult than expected for a well-structured navigation. What possibilities does Sharepoint offer to link the subprocesses with their corresponding main process and to display them in a well-structured navigation? Is this possible with built-in tools or what has to be used? Are there extensions or technologies (Powershell, SPFx), with which this project could be tackled?

In all chances there are alternative solutions available, which cover the desired requirements in a more optimal and easier way. Gladly I am also open for such suggestions from your side.

Best regards

Sifug