Prepared for Ellen
Ellen, the watermark is in the video file
Which means no account or upload change will remove it, and it explains why nothing you tried worked. Here is what actually fixes it.
What you already told us settles it
You said the watermark shows up whichever platform you use. A platform can only print its own account name, so a mark that survives the move from YouTube to Vimeo is inside the video file itself. That is why re-uploading and changing settings kept doing nothing.
Or if you would rather just talk it through, the assistant below knows your situation and goes to the same place.
Ask about your video
Assistant
Hi Ellen. I have your situation already, so no need to repeat any of it. Since the watermark follows the video across platforms, it is in the file, and the fix is getting a clean copy from whoever made it. Tell me who produced the video and I will help you ask for exactly the right thing.
Why the usual advice does not work here
Nearly everything written about this addresses the other version of the problem, where the platform prints your channel or uploader name around the player. That is fixed by uploading from a differently named account, and it is genuinely a ten minute job.
It is also irrelevant when the mark is inside the file. No account, no upload, no setting and no platform reaches into the pixels. That is why careful instructions kept producing no change, and it is not a sign you did anything wrong.
What actually fixes it
A clean export from whoever made the video. Branded and unbranded versions are a standard deliverable in real estate video, so most producers already have one sitting in the project. It is usually a short favour rather than a re-edit.
One thing worth checking first, because it costs nothing: if the mark only appears in an intro or an end card rather than throughout, trimming those few seconds may be the whole fix.