Files

Everything the server keeps is in the data folder, ~/.local/share/uniform-chat-server by default (under $XDG_DATA_HOME when set):

File	Contents
server.db	The SQLite database: accounts, devices, rooms and messages. The server updates it to its current layout at start.
server.db-wal, server.db-shm	The database's write-ahead log and its index, while the server runs; at a clean stop the log is written into server.db. Copy them with the database.
media/	Uploaded files, and the thumbnails made from them in media/thumbnails/.
signing.key	The server's private signing key, which signs every event it creates. It is created when first needed and readable only by your user.
logs/	One log file per start of the server, named by the time it started, e.g. server-20261110-104027.log; the newest 20 are kept. With Storage:LogDirectory they are elsewhere: the apt package's service writes them to /var/log/uniform-chat-server.

To back up the server, stop it and copy the whole folder. Keep signing.key with the database and keep it private: it is the server's identity.