https://mariushosting.com/how-to-install-transmission-on-your-synology-nas/

Transmission is designed for easy, powerful use. Transmission has the features you want from a BitTorrent client: encryption, a web interface, peer exchange, magnet links, DHT, µTP, UPnP and NAT-PMP port forwarding, webseed support, watch directories, tracker editing, global and per-torrent speed limits, and more. In this step by step guide I will show you how to install Transmission on your Synology NAS using Docker.
Install Docker via Synology “Package Center”.
Go to File Station and open the docker folder. Inside the docker folder, create one new folder and name it transmission. Follow the instructions in the image below.Note: Be careful to enter only lowercase, not uppercase letters.
Now create three new folders inside the transmission folder that you created at STEP 3 name data, downloads, watch. Follow the instructions in the image below.Note: Be careful enter only lowercase, not uppercase letters.
Go to Control Panel / Task Scheduler / Create / Scheduled Task / User-defined script. Follow the instructions in the images below.
Once you click on User-defined script a new window will open. Follow the instructions below:
docker run -d --name=transmission \\
-p 9091:9091 \\
-p 51413:51413 \\
-p 51413:51413/udp \\
-e PUID=1026 \\
-e PGID=100 \\
-e TZ=Europe/Bucharest \\
-e USER=marius \\
-e PASS=mariushosting \\
-v /volume1/docker/transmission/data:/config \\
-v /volume1/docker/transmission/downloads:/downloads \\
-v /volume1/docker/transmission/watch:/watch \\
--restart always \\
ghcr.io/linuxserver/transmission