Background
3+YOE (1y not really related)
MS from top 20 school in the world, not in CS
Don't have work authorization in country of application
Don't speak local language natively
1750 elo on Leetcode

Timeline
Mid January: applied for 3-4 SWE roles on Bytedance's English careers page
Late January: got an email inviting me to do an online assessment on Hackerrank (details below) and completed it more or less right away
Late January: scheduled an interview for early February
Early February: Virtual onsite interview over Lark (Bytedance's Google Suite clone)... details below

Hackerrank Online Assessment
These questions may not have been chosen by Bytedance and may just be general Hackerrank problems.

I don't remember specifics of Q1 or Q2, but they were both ad hoc problems like Q1s on the weekly contest. Q3 was Path with minimum effort. Q4 was an annoying string parsing problem. Something like, you get a string and have to parse all of the fractions in the string depending on whether or not they meet some long list of requirements or not. I got Q1-3 within about 20-30 minutes, but didn't solve 4 (time limit was 2h).

Q1: Easy
Q2: Easy, Easy-Medium
Q3: Medium-Hard
Q4: I felt like it was a Medium difficulty problem, but idk cause I didn't solve it

Virtual Onsite
The interview was straight to the point -- no friendly chatting and he didn't give me a single hint, even when I asked for hints on Q1. Also, the interviewer didn't have a coding platform to use so he asked me to share my screen and use a text editor on my computer -- this seemed like a bit of a red flag in terms of preparation by the interviewer. Once that was sorted out he asked me to introduce myself and then got straight into the techincal questions.

Q1. Write a decorator that reads the error of the function it decorates and outputs that error to a log file.

This question really caught me off guard. I have never written a custom decorator before and also do not know how to read the standard out from a function and save it into a log file. Needless to say, I don't think this question went very well.

Q2. Decscribe TCP handshakes.
I probably should have had a better answer for this. Also, didn't feel confident in my answer for this one.

Q3.
Write a function that takes two numbers in base-40, sums them, and returns the sum in base-40.

He didn't have any test case examples for me so I made my own base-40 numbers using the alphabet from a-Z. I converted them to decimel, added and then converted back. My solution worked, but he didn't seem too positive on it. I guess he was expecting me to solve it without converting to decimel, but idk.

Feelings on the interview
Overall I would say I have a good impression with Bytedance (Applications were good, online assessment was good, HR was good), but not so good with the specific interview. I felt the interviewer and I were both underprepared and it made out to be a difficult interview.

I didn't finish the interview feeling super confident and should probably get back to studying :(