SPK for Synology is available here:
https://synocommunity.com/package/radarr

Synology DS414 uses armv7l CPU MARVELL Armada XP MV78230

Manual update when auto-update fails:

synopkgctl stop radarr

cd /var/packages/radarr/target/share/
sudo mv Radarr Radarr-old
sudo mv /tmp/radarr_update/Radarr .
sudo chown -R sc-radarr:radarr /usr/local/lidarr/

synopkgctl start radarr