On Ubuntu(Debian based) have added Tor repo:
cat > /etc/apt/sources.list.d/tor.list <<EOF
deb https://deb.torproject.org/torproject.org $(lsb_release -cs) main
EOF
Then "apt update" shown:
Err:4 https://deb.torproject.org/torproject.org focal InRelease
The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 74A941BA219EC810
I have found the command which also failed (gpg: keyserver receive failed: No name):
# sudo apt-key adv --recv-keys --keyserver keys.gnupg.net 74A941BA219EC810
Executing: /tmp/apt-key-gpghome.ZVqDt5Gg6d/gpg.1.sh --recv-keys --keyserver keys.gnupg.net 74A941BA219EC810
gpg: keyserver receive failed: No name
i red here that it means that server (keys.gnupg.net) is not working, so i have to use different one, which complained "new key but contains no user ID - skipped":

# sudo apt-key adv --recv-keys --keyserver keys.openpgp.org 74A941BA219EC810
Executing: /tmp/apt-key-gpghome.uXWrm9Keq6/gpg.1.sh --recv-keys --keyserver keys.openpgp.org 74A941BA219EC810
gpg: key EE8CBC9E886DDD89: new key but contains no user ID - skipped
gpg: Total number processed: 1
gpg: w/o user IDs: 1
What WORKED was server keyserver.ubuntu.com:

# sudo apt-key adv --recv-keys --keyserver keyserver.ubuntu.com 74A941BA219EC810
Executing: /tmp/apt-key-gpghome.qLK66YYDIF/gpg.1.sh --recv-keys --keyserver keyserver.ubuntu.com 74A941BA219EC810
gpg: key EE8CBC9E886DDD89: 1 duplicate signature removed
gpg: key EE8CBC9E886DDD89: public key "deb.torproject.org archive signing key" imported
gpg: Total number processed: 1
gpg: imported: 1
Then installing, updating the package tor worked:
apt update;apt upgrade