alt Hacker NewsVivaldi 8.1 still supports it (Chromium 150) as loaded unpacked extension.
Edit: and latest August 14, 2026 Chromium 152.0.7977.38 based Snapshot https://vivaldi.com/blog/desktop/address-field-calculator-an... has this in patch notes:
"[Extensions] Re-enable and extend Manifest V2 extension support for the time being (VB-130324)"
I wouldn't be sure this is a long term solution. Maintaining a this into perpetuity would probably take a lot of resources that Vivaldi team might not have.