Hi, @sns ,
I will suggest you to recreate the web part as SharePoint Add-in or SPFx web parts. In SharePoint Online, code-based sandbox solution (.wsp files) has been deprecated for long time.
Intro on add-ins: https://learn.microsoft.com/en-us/sharepoint/dev/sp-add-ins/sharepoint-add-ins?redirectedfrom=MSDN
SPFx: https://learn.microsoft.com/en-us/sharepoint/dev/spfx/sharepoint-framework-overview
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