This is becoming quite an issue. Figma and Microsoft products (Sharepoint specifically) continue to add themselves automatically to Login Items. I delete from Login Items. I remove them from the dock. I remove them from running in the background, and, yet, each time I start them, they add themselves to Login Items.
[Edited by Moderator]
Mac mini, macOS 15.3
Modern Login Agents are built into the app itself and simply register with the OS (which is when they show up in Login Items). The controls for whether the app starts automatically on login (and registers) should be in the application's own preferences.
Microsoft tends to play poorly in this sense because it actually has multiple "Login Items" - one for checking for activation/licensing, one for checking for updates, one for One Drive that is separate from other Office products...not sure about the other one you mentioned, though.
These do not have a setting to turn it off. In both cases, they are adding agents to the Login Items, not the app itself. I am not asking a question with a simple answer - and it appears to apply to all applications on the Mac. The OS allows applications to add items to the Login Items without having to ask for permission.
FWIW, there is a very simple solution. If you don't like how certain third-party apps work in macOS, stop using them.
I don't use Figma or Microsoft products but usually, apps that add themselves to Login have their own setting to log in automatically.
How to prevent apps from adding themselves to Login Items
