Hi @adil ,
As this post mentioned, you could rebuild the solution.
1- Open the custom SharePoint Project in your VS.
2- remove old references (.SharePoint.dll) (.sharepoint..dll) and add new references (.SharePoint.dll) (.sharepoint..dll).
3- rebuild the solution .
4- add , deploy, and install the sp solution on the new env.
Another similar post for your reference:
Migrating Custom Solutions from SharePoint 2013 to 2019
And when it comes to third-party products, I would suggest you seek help from third-party suppliers.
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