Love how the senior dev said 'this is a simple fix' and it has now consumed three days of my life, two liters of coffee, and the last remnants of my sanity.

Can you share the gist of the problem? I love a good unsolvable mystery.

Talk to the Senior, and ask for help.

I once had the same thing happen, with the junior getting lost in the infra code, instead of doing a simple parameter change inthe BizLogic.

I think that means you're learning

That sounds exactly like programming! Yeah.. they're so institutionalized into their lack of self-respect that to them it's just normal and simple.

"Haha yeah let's change the entire company's tech stack, hardware and software, in 48 hours, np"

Yeah as the others said, ask what they thought the fix would be and explain where you're getting stuck

Could be that it is or should be. Can also be that there is hidden complexity or something the senior didn't think about and why the solution in the seniors head does not work or is a lot harder to achieve.

As others said without details it's hard to say what's up. At least talk to the senior before spending that much time. See if you have the same approach and validate it with the senior.