How to exit Win11 Insider Preview Build 26220?

I accidentally joined the Windows Insider Program and opted out in Settings, but I'm not sure if it worked.

My desktop still shows the watermark: "Windows 11 Home Insider Preview Evaluation Copy. Build 26220.8764".

My question:

Will my system automatically become the official release after the evaluation expires?

If not, how can I return to the official version without losing personal files? Do I have to clean install?

If I stay on this build, will I ever receive official cumulative updates again (like future 26H1 updates)?

I'd really appreciate any professional advice. Please reply below or PM me. Chinese replies are welcome!