Learn English – Word for a topic with an unreachable conclusion

To address your second question, I would go with Model Parameters. I've been a technical writer for over 20 years and one of my first lessons as a technical writer was to avoid the saxon genitive if at all possible. For example, use "the cards on the shelf" instead of "the shelf's cards". It's more concise and clearer for your reader. I would especially avoid the saxon genitive in a title. If you consider a table of contents where multiple titles are structured as saxon genitives, it becomes difficult to read very quickly.

I have less of an issue with "the user's password", but I still wouldn't use "User's Password" in a title. "User Password" is more concise.

You could use controversial.

Per Merriam-Webster:

controversial adjective

: relating to or causing much discussion, disagreement, or argument : likely to produce controversy

Examples of Controversial

• Abortion is a highly controversial subject.
• a decision that remains controversial
• He is a controversial author.

Some other alternatives would be:

• contentious
• disputed/disputable
• polemical