Applying for new job in same company etiquette

[workworrier]

I have been in my current role for 3 months. Before that I was out of work for a period of time due to health problems and was unable to work. I started a new job in October. I really like it, however I feel like I don’t really have much of a “purpose” and today someone who works from the place I work (but isn’t a co-worker - can’t give too much away as it may be identifying) expressed how my job role wasn’t important and they “got along fine” when nobody was in the role before I was employed.
Somebody brought to my attention a job within the same company but a different area yesterday. It’s more suited to my experience, I feel I would be able to make a proper career out of it and would have my own workload etc where I would have a real purpose. It’s also a higher grade so more money which would really help. I have applied for the job.

I’m now panicking that if I get offered an interview and I discuss this with my line manager that I will get sacked. I wasn’t actively seeking other work and wouldn’t have been doing if someone hadn’t pointed this other job out to me.
What do I do? If I don’t get an interview nobody will know, but if I was to get an interview and not get the other job, I’m worried I will be sacked for applying to another job.
I’ve never had to do this before and my anxiety is getting the better of me because I’m overthinking it all

I would let your line manager know asap that you have done it. I think the best etiquette would be to let them know in advance but unless you can play it like "ive seen a really great opportunity, im going to apply, just wanted to let you know" and hope they dont find out the dates somehow, then just asap is best.

If you arent successful and you end up in the current role for a while then you would want to avoid any bad feeling im sure.

But im no expert and am also looking internally so im keen to see what others say

Does your company have policy on internal transfer? If yes, have a look. For example - we have automatic notification to line managers if anyone apply for an internal job. Either way, I would speak to your line manager asap.

Our internal applications automatically notify your current line manager. Also, you have to have been with the company for a minimum of one year, though they can make exceptions. Definitely speak to your line manager. If they're supportive, speak to the hiring manager, too. Even if they're not supportive, speak to the hiring manager, from the perspective of future interest - what could you do to improve your chances for a future application, training or experience? Make them aware of you and your interest.