Hi,
Thank you for sharing your question. I get why that's annoying! It's a pain when you wanna tweak a setting, and it's just gone, mainly because it messes with your emails.
Based on my knowledge the new Outlook doesn't have the Trust Center. You won't find it. That's only in the old-school Outlook. If you need to mess with those settings (security, downloads, etc.), you will have to go back to the Classic Outlook, head to File > Options > Trust Center > Trust Center Settings. Change what you need to change. Some stuff might stick when you go back to the New Outlook, but you gotta do it in the Classic version because the new one doesn't do it yet.
May I also ask have you tried switching back to the Classic Outlook to fix it? If not I can walk you through it.
Let me know how it goes or if you get stuck switching back. I'm here to assist in getting it all set up right.
Best Regards,
Noel