Hi @Nick Ryan,
I know that I simply have to open each in Visual Studio, change the target server to 2022 and save but there are a huge number of them so that's a big job.
It is done just once on a SSIS Project level, not on the individual SSIS package level, via TargetServerVersion setting value. Please see below. It is better to migrate your SSIS Projects in Visual Studio manually. It can show some potential errors and bugs. When you are deploying SSIS project for SQL Server 2019 to SSIS run-time server 2022, that switch/migration to SSIS 2022 is happening anyway behind the scenes.
Maybe recompile scripts with a new .NET version?
SSIS is using up to the latest version of the earlier .Net Framework v.4.8. It cannot use .Net Core versions 5,6,7,or 8.