Error

$ flatpak --user --no-gpg-verify remote-add --if-not-exists flathub https://dl.flathub.org/repo/flathub.flatpakrepo

error: Can't load uri https://dl.flathub.org/repo/flathub.flatpakrepo: While fetching https://dl.flathub.org/repo/flathub.flatpakrepo:

[60] SSL peer certificate or SSH remote key was not OK

Solution

sudo apt update

sudo apt install ntpdate

sudo ntpdate pool.ntp.org