If only I had had this chance yesterday.
&
If only I would had this chance yesterday.

What is the difference?

Question

If only I had had this chance yesterday.
&
If only I would had this chance yesterday.

What is the difference?

Answer

The second is a bad sentence. "Would" needs to be followed by an infinitive.  "Would had" never makes sense.

Answer

The second can be corrected by:
If only I would have had this chance yesterday

The meanings aren’t very different.

Answer

The first one is in the Past Perfect tense. The second one isn't a valid construction.