Earlier quoted context omitted.
When I was in a similar situation I ended up paying for a few hundred dollars worth of acoustic foam for the walls. It didn’t stop everything, especially stopping noise from upstairs neighbors, but it was still a huge help. It’s unsightly though. The kinds that are actually nice to look at as wall decoration are super expensive.
Did you do a before and after dB measurement? I'm curious on quantitatively how well it worked as I was thinking of doing the same thing but I talked to a few musician buddies and read many things like https://acousticalsolutions.com/how-to-soundproof-acoustic-f... & https://soundproofcentral.com/soundproof-foam/ and all seem to agree foam stuck on a wall is for echo not soundproofing so didn't try it out. Also many…
It's usually possible to make a positive difference, but if it's a serious problem a workable fix - better, but not perfect - will eat up a lot of room space.
The real problem is that most apartments and houses are built cheaply and building codes for acoustic isolation aren't nearly aggressive enough. They seem to stop at the level which makes conversations hard to hear, which isn't much help when people have TVs and/or subwoofers.