Multiple issues installing (Linux Mint 20.3)

[TernaryC]

I've been having a lot of troubles trying to install and use Lyrebird. I've tried both approaches.

1. Installing via .deb (both v1.10 and v1.20), gives the error "Dependency is not satisfiable: python3-toml". I do, in fact, have the toml python package, as installed via pip, but this is apparently not good enough. I cannot find any way to install a package called "python3-toml", through apt or otherwise. No package is found, full stop.
2. Installing via .tar.gz (v1.20), running install.sh throws no errors. Subsequently running lyrebird, or running the lyrebird file or app.py inside the extracted .tar.gz, grants the following error: "SoX is missing the PulseAudio audio driver." Running sudo apt install libsox-fmt-pulse returns 404 errors which I cannot seem to fix.

I'm at a loss as to what to do about either of these, unfortunately.

Transcript of the 404 errors mentioned in point 2 above

$ sudo apt install libsox-fmt-pulse
Reading package lists... Done
Building dependency tree       
Reading state information... Done
The following NEW packages will be installed:
  libsox-fmt-pulse
0 upgraded, 1 newly installed, 0 to remove and 12 not upgraded.
Need to get 7,396 B of archives.
After this operation, 54.3 kB of additional disk space will be used.
Err:1 http://security.ubuntu.com/ubuntu focal-security/universe amd64 libsox-fmt-pulse amd64 14.4.2+git20190427-2+deb11u2build0.20.04.1
  404  Not Found [IP: 91.189.91.83 80]
E: Failed to fetch http://security.ubuntu.com/ubuntu/pool/universe/s/sox/libsox-fmt-pulse_14.4.2+git20190427-2+deb11u2build0.20.04.1_amd64.deb  404  Not Found [IP: 91.189.91.83 80]
E: Unable to fetch some archives, maybe run apt-get update or try with --fix-missing?

OS: Linux Mint 20.3 Cinnamon 5.2.7
Linux Kernel: 5.15.0-76-generic