Only 19 givens, but there is no strong correlation between the difficulty and the number of givens. Note that no 4 is given, and only one 5.

First we spot that a 3 can be filled in:

and another 3:

and a third 3:

and a fourth 3:

Let us mark some pairs for possible future use.

So far for the 3's. There is also a 6 in the upper left hand corner:

and another one in the lower left hand corner:

and another one:

Adding a few pairs:

.. (continued) ..