I don’t know if this a bug or even if it’s recent, but on one of my macs, the safari extension button in the toolbar is gone. It’s there on the other one. Both machines are running macOS 15.5, Safari 18.5, and Bitwarden 25.5.1. Both have the Bitwarden extension enabled. The only difference I can tell is that the working one is an M2 and the non-working one is an Intel. I definitely seem to remember seeing the button recently, but did restart the machine lately.
Try right-clicking the Safari toolbar and selecting “Customize Toolbar” — you might be able to drag the Bitwarden icon back in.
Unfortunately, the Bitwarden icon isn’t visible in the Customize Toolbar window.