Install

Prefer your distro's package manager (PEP 668 blocks system-wide pip on most modern distros):

# Debian / Ubuntu
sudo apt install python3-pygls

# Fedora
sudo dnf install python3-pygls

# openSUSE
sudo zypper install python3-pygls

# Arch (AUR or community)
sudo pacman -S python-pygls

Fallback (use a venv or --user):

pip install --user pygls

To check that it starts, open a shell in your tango-remixer checkout (the folder that has lsp/ in it; as a submodule, typically resources/tango-remixer/) and run:

python3 -m lsp

Nothing is printed: the server waits for LSP messages on standard input. Silence means pygls was found; an ImportError means it was not. Ctrl-C stops it. That is the only time you start it by hand: editors launch it themselves and talk to it over stdio.