Administrator-Approved InfoPath Form Fails to Upload After Upgrade to Subscription Edition

Thank you for the clarification regarding the InfoPath Forms Services support lifecycle.

I understand that InfoPath Forms Services is now outside of Microsoft's support window and that the long-term recommendation is to migrate these solutions to Power Apps or another supported platform.

However, in our case, this is a migration of an entire SharePoint web application from SharePoint 2019 to SharePoint Server Subscription Edition. The business requirement is to keep the existing InfoPath forms operational during the migration phase and then modernize them afterward.

The same administrator-approved, browser-enabled managed-code form currently works in our SharePoint 2019 environment. My immediate objective is to understand why the form fails validation in SharePoint Subscription Edition with the following error:

Could not load file or assembly

'Microsoft.Office.InfoPath, Version=16.0.0.0'

Given that SharePoint SE still allowed InfoPath Forms Services to function prior to the support end date, I am trying to determine whether this is:

• A form code assembly/version mismatch issue
• A missing dependency on the SharePoint SE servers
• A change in how administrator-approved forms are validated in SharePoint SE
• A known migration issue when forms are republished from InfoPath 2010

I'm not looking for a long-term workaround such as installing unsupported components on the farm. Rather, I'm hoping to identify the root cause of why a form that worked in SharePoint 2019 cannot be uploaded to SharePoint Subscription Edition so that we can keep the application operational while we plan its eventual migration to Power Apps.

Has anyone successfully migrated administrator-approved managed-code InfoPath forms from SharePoint 2019 to SharePoint Subscription Edition and encountered this particular assembly loading error?