The correct generic is PropertyBuilder<TProperty> (i.e. no constraints on the type of T)
public static PropertyBuilder<TProperty> ForSqlServerHasDefaultValueSql<TProperty>(this PropertyBuilder<TProperty> propertyBuilder, string sql)
public static PropertyBuilder<TProperty> HasDefaultValueSql<TProperty>(this PropertyBuilder<TProperty> propertyBuilder, string sql)
However SQLite extensions are defined as PropertyBuilder<TEntity> and TEntity is constrained to a reference type. The T should be renamed and the constraint removed.
public static PropertyBuilder<TEntity> ForSqliteHasDefaultValueSql<TEntity>(this PropertyBuilder<TEntity> builder, string sql) where TEntity : class;
This causes compilation errors if you try to set a default value for SQLite on a property that is a value type.