To go through this interview process even though I'm happy in my current role

[Onlyrainbows]

Recruiter got in touch via LinkedIn. I just wanted to know what they'd offer and to benchmark my current salary, which surprisingly is not that competitive (recruiter is offering a 40% pay increase).

Last week my role was close to being my manager's deputy (director role) and I would love to have her role one day.

So I think if I play my cards right once she gets promoted (or leaves) I would just inherit her role.

Of course one side of me is greedy and thinks that the pay increase is worth it, and I feel a bit hesitant about that. But would it be a massive waste of time if I'm not necessarily interested in this role the recruiter is offering to me?

Sorry, not sure I understood. If your salary isn't competitive now what makes you think it would be at a higher level with the same company?
What do you mean by your "role was close to the manager's deputy"? So it's not now?
What if she doesn't get promoted or leave for another few years? Unless you think her leaving is imminent. Even if she leaves, you have no guarantee you would get the job.
I would go for the interview and see what the job entails. (Again, it doesn't mean you get it). Even if it's offered to you, you can decide to stay put. If you decide to leave you could still apply for your manager's job if and when she leaves but at least you would be on a better salary (provided it's still a job you like doing).

You would be unreasonable to interview for a role you had no intention of taking

You are wasting everyone’s time. If you want to benchmark your current salary you can just ask a recruiter for this and they would normally help.

I love my role! I love my manager but thing is, I've only been 6 months in my current company.

I know that going through the process doesn't mean I'll get an offer.

My DM thinks it's stupid to even think of changing jobs when "I'm still learning".

How much experience do you have of the role?

Within this exact role 6 months. Of transferable experience 10+ years.