The goalkeeper finds the ball first with his hands, is it a penalty?

Yes, this should've been a penalty.

Goalkeeper did come first to the ball, but he drops it, and after that, he trips player who was possibly in a good position to score a goal.

Most likely, this is not a foul by either player.

Neither player appears to act in a way to meet any of the requirements for a direct free kick that would be relevant, as Law 12, section 1 Direct Free Kick defines the three manners as

Careless is when a player shows a lack of attention or consideration when making a challenge or acts without precaution. No disciplinary sanction is needed

Reckless is when a player acts with disregard to the danger to, or consequences for, an opponent and must be cautioned

Using excessive force is when a player exceeds the necessary use of force and/or endangers the safety of an opponent and must be sent off

It looks worse because

1. the attacker is running at high speed, and the goalkeeper's movement crosses theirs, rather than being in the same direction

2. the attacker embellishes the result of the contact between the players, grasping the knee and curling up instead of attempting to shield his face or body while falling to the ground

but both players have taken due care in attempting to play the ball:

• the attacker is attempting to move himself and the ball away from the goalkeeper, not towards

• the goalkeeper has slowed and places only their hands in the path of the ball and attacker

• any contact is minimal and barely distinguishable from the contact of each player on the ball alone

---

It is more arguable that this is an offence by the attacker, as at the moment of contact, the goalkeeper has both hands on and around the ball.

In this situation, at the professional level, a first-team goalkeeper would be expected to easily hold the ball as they slide down to the ground.

Law 12, section 2 Indirect Free Kick states

A goalkeeper is considered to be in control of the ball with the hand(s) when:

• the ball is between the hands or between the hand and any surface (e.g. ground, own body) or by touching it with any part of the hands or arms, except if the ball rebounds from the goalkeeper or the goalkeeper has made a save
• holding the ball in the outstretched open hand
• bouncing it on the ground or throwing it in the air

A goalkeeper cannot be challenged by an opponent when in control of the ball with the hand(s).

As the attacker has kicked the ball while it fulfills the definition of on control above, they have breached the law. The appropriate restart would be an indirect free kick awarded to the goalkeeper's team.