I encountered an issue where adding a Migration after changing the CLR type of a property mapped to a Computed Column in SQL Server results in the Migration trying to ALTER COLUMN on that column which doesn't work.

Example, start with the following class and DbContext:

public class ComputedDbContext : DbContext
{
    public DbSet<FileData> Files { get; set; }

    public ComputedDbContext(DbContextOptions<ComputedDbContext> options) : base(options) { }

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        base.OnModelCreating(modelBuilder);

        modelBuilder.Entity<FileData>(entity =>
        {
            entity.Property(e => e.FileSize)
                .HasComputedColumnSql("DATALENGTH([FileContents])");
        });
    }
}

public class FileData
{
    public int FileDataId { get; set; }
    public byte[] FileContents { get; set; } = Array.Empty<byte>();
    public int FileSize { get; set; }
}

Then add an initial migration:
Add-Migration Initial

This creates the table with computed column:

CREATE TABLE [Files] (
    [FileDataId] int NOT NULL IDENTITY,
    [FileContents] varbinary(max) NOT NULL,
    [FileSize] AS DATALENGTH([FileContents]),
    CONSTRAINT [PK_Files] PRIMARY KEY ([FileDataId])
);
GO

Later, realize a problem because DATALENGTH returns BIGINT so the type of FileSize in the class needs to be changed:
public long FileSize { get; set; }

Add another migration:
Add-Migration DataTypeChange

This generates:
ALTER TABLE [Files] ALTER COLUMN [FileSize] bigint NOT NULL;

Which fails when updating the database with:

Cannot alter column 'FileSize' because it is 'COMPUTED'.

This requires removing the AlterColumn call from the migration after creating it in order for future migrations to run successfully. I don't believe properties with .HasComputedColumnSql() configured should be picked up by migrations when their CLR type changes since the database column has no type itself in this case.