What migration strategies exist for gradually moving a large .NET Framework application to modern .NET rather than a big-bang rewrite?

Common incremental strategies include: the 'strangler fig' pattern (build new features in modern .NET services alongside the legacy Framework app, gradually routing traffic away from old code), multi-targeting a shared class library to both net48 and net8.0 during a transition period to catch incompatibilities early, or splitting a monolith into a modern .NET API layer in front of a legacy Framework backend that's migrated piece by piece.

<!-- A shared library multi-targets both during transition -->
<TargetFrameworks>net48;net8.0</TargetFrameworks>

<!-- Conditional code for framework-specific APIs -->
#if NETFRAMEWORK
    // Framework-specific code
#else
    // Modern .NET code
#endif