https://updates.duplicati.com requires at least TLS 1.2, as earlier versions have security problems.
If I recall corrctly, the previous updates host was more forgiving (and got dinged by security scans).
You could try the above link in Internet Explorer to see if fails too. Windows 7 defaults to no TLS 1.2.
Enabling TLS 1.2 on Windows 7 are some third party directions that link to some old Microsoft data.
Windows 7 support ended on January 14, 2020 so you’re living dangerously, and ought to get off it…
You’re not getting security updates from Microsoft now, so there’s no telling what bad stuff will get in.
If you really want to stay with it, you could visit Duplicati Downloads.to run an .msi installer manually.