‘It is more blessed to give than to receive.’ isn't in the bible.

Last, in Acts 20:35 Paul told people “to remember the words of the
Lord Jesus, how he said, ‘It is more blessed to give than to receive.’”
Since Jesus never made such a biblical statement, isn't Paul guilty of
deception?

Biblical Errancy Pamphlets by Dennis McKinsey Pamphlet 1 Q24.

Answer:

(Acts 20:35 NIV) In everything I did, I showed you that by this kind of hard work we must help the weak, remembering the words the Lord Jesus himself said: 'It is more blessed to give than to receive.'"

The saying was part of the oral tradition of Jesus sayings, Paul even alludes to this by saying "remembering the words the Lord Jesus himself said". They do not have to be recorded in the bible to be true. Even John admits that not everything Jesus did was written down.

(John 20:30-31 NIV) Jesus did many other miraculous signs in the presence of his disciples, which are not recorded in this book. {31} But these are written that you may believe that Jesus is the Christ, the Son of God, and that by believing you may have life in his name.

(John 21:25 NIV) Jesus did many other things as well. If every one of them were written down, I suppose that even the whole world would not have room for the books that would be written.

The bible also records that Paul knew Peter, and James personally (Acts 21:18 ), Paul stayed with Peter for fifteen days (Gal 1:18,19, 2:9). Paul also lived at a time when there were 500 eyewitnesses to the resurrection, most of whom were still living (1 Cor 15:5). He also spent time with Mark and Luke who wrote two of the gospels. (Acts 12:25, 2 Tim 4:11).

The words relate to Luke 6:38 and pertain to the spirit of Jesus teaching.

(Luke 6:38 NIV) Give, and it will be given to you. A good measure, pressed down, shaken together and running over, will be poured into your lap. For with the measure you use, it will be measured to you."

(Luke 12:33 NIV) Sell your possessions and give to the poor. Provide purses for yourselves that will not wear out, a treasure in heaven that will not be exhausted, where no thief comes near and no moth destroys.