once found a bug in an outdated sdk we were using that made an enpoint take 10 seconds. after passing one extra param to the function from that sdk it went down to 30ms

So i wasted last 24 hours trying to satisfy my ego over a shitty interview and revisiting my old job's codebase and realising that i still don't like that shit. just i am 25 and have no clue where am i heading at. i am just restless, my most of the decisions in 2023 have given very bad outcomes and i am just trying doing things to feel hopeful.

context for the interview story-----
my previous job was at a b2b marketing company whose sdk was used by various startups to send notifications to their users, track analytics etc. i understood most of it and don't find it to be any major engineering marvel, but that interviewer was very interested in asking me to design a system around it.

in my 1.2 years of job there, i found the codebase to be extremely and unnecessarily verbose ( java 7) with questionable fallbacks and resistance towards change from the managers. they were always like "we can't change it otherwise a lot of our client won't use our sdk". i still wrote a lot of testcases and tried to understand the working of major features.

BTW, before you guys go on a declare me an embarrassment of an engineer who doesn't know the product's code base, let me tell you that we are talking SDKs (plural) and a service based company here. their was just one SDK with interesting, heavy lifting stuff and 9 more SDKs which were mostly wrappers and less advanced libraries. i got tasks in all of them, and 70% of my time went into maintaining those and debugging client side bugs instead of exploring the "already-stable-dont-change" code base.

so based on my vague understanding and my even more vague memory from 1 year ago, i tried to explain an overall architecture to that interviewer guy. His face was screaming the word "pathetic" from his expressions, so i thought that today i will try to decode the codebase in 12-15 hours, publish a cool article and be proud of how much i know a so called martech system design. their codebase is open sourced, so it wasn't difficult to check it out once more.
but boy oh boy i got so bored. unnecessary clases , unnecessary callbacks static calls , oof. i tried to refactor a few classes, but even after removing 70% of codebase, i was still left with 100+ classes , most of them being 3000-4000 files long. and this is your plain old java library adding just 800kb to your project.

boring , boring stuff. i would probably need 2-3 more days to get an understanding of complete project, although by then i would be again questioning my life choices , that was this a good use of my 36 hours?

what IS a correct usage of my time? i am currently super dissatisfied with my job, so want to switch. i have been here for 6 months, so probably i wouldn't be going unless i get insane money or an irresistible company offer. For this i had devised a 2 part plan to either become good at modern hot buzz stuff in my domain( the one being currently popularized by dev influenzas) or become good at dsa/leetcode/cp. i suck bad at ds/algo stuff, nor am i much motivated. so went with that hot buzz stuff.

but then this interview expected me to be a mature dev with system design knowledge... agh fuck. its festive season going on and am unable to buy any cool shirts since i am so much limited with my money from my mediocre salary and loans. and mom wants to buy a home too... yeah kill me