Ubuntu Linux, Unable to set bitcoin datadir to a folder in different drive
Applications in a Snap run in a container with limited access to the host system, you can install bitcoin-core with full filesystem access via the Luke-Jr repository:
sudo add-apt-repository ppa:luke-jr/bitcoincore
sudo apt-get update
sudo apt-get install bitcoin

or download the release from here:https://bitcoincore.org/bin/bitcoin-core-0.21.0/bitcoin-0.21.0-x86_64-linux-gnu.tar.gz
unpack and run bitcoind executable inside the bin folder.