The difference between Deathmatch and Team Deathmatch is that the agent you choose actually plays a role in Team Deathmatch. When loading into a regular deathmatch, the agent is chosen for the player as players aren’t able to use their abilities so it doesn’t matter which agent someone uses. On the other hand, players specifically choose agents when loading into a team deathmatch as abilities are usable.
In Team Deathmatch, players respawn shortly after being eliminated, allowing for continuous action throughout the game. Respawns happen near teammates and away from enemy sightlines to reduce spawn camping and provide players with a fair chance to re-engage.