How can I stop the cranshaft pulley of my Lexus IS300 (2002) to unscrew the bolt ?

Shouldn't need to remove. Bolt on side that adjusts tension. Release tension buy turning bolt counterclockwise . Tensioner should move toward engine and release belt.

2002 frontier 4 cyl: 1) take off air intake tube, 2 screws 13 mm above radiator. 2) 1st belt for power stirring has pulley, undo pulley screw and unscrew adjuster bolt enough to take belt off 3) 2nd belt for alternator and water pump has no pulley but adjusting bolt and mounting bolt on alternator pulley, loosen mounting bolt and unscrew adjusting bolt enough to take belt off, if alternator will not move go under the truck and remove plastic cover- 6 screws 13 mm heads, after that look directly under alt. Pulley and should see a screw head 9/16 in, loosen it so alternator can move, now should be easy to remove belt ( it will be a lot harder to put new one though) 4) 3rd belt for compressor has pulley so follow #2 to remove it ,have to be done under the truck. First 2 belts will have to work around fan blades to remove them so wear gloves. After replacing belts remember that not to over tighten bolt on pulleys.

Get a breaker bar and posision it against a chassis rail or something solid. Tap ignition key to start & quickly off. The starter motor will crack the bolt loose for you. Just make sure the bar wil not damage anything (such as radiator but yours front whee drive right? radiator be ok but get my drift.

Take the bolt out, clean it and the bolt hole and replace the bolt with some Loctite on the threads. Use medium strength so that the bolt can be removed when needed.

Loosen the lock bolt on the upper part of the tensioner(arrowed in black). Release tension on the belt at the tensioner(arrowed in red) by turning counter clockwise on the pulley nut as indicated in blue.
Slip the belt off the pulleys while keeping pressure on the tensioner. Refit the new belt and make sure it is properly located on all the pulleys before releasing pressure on the tensioner. Tighten the lock bolt.
The tensioner is self adjusting you just need to make sure the belt is properly seated on all the pulleys before tightening the lock bolt.
The exact position of the tensioner varies on the different engines but the routing is the same and it is always between the alternator and power steering pulleys on the gas engines.
C - Cranshaft
A - AIR pump
Alt - alternator
W - Water pump
P - Power steering
A/C - airconditioning

I think because your searching for a pulley which is bolted to the AC clutch assembly. AC clutch bearing assembly is what you need

It is tough to remove if you are working from home without air-wrench. Sometimes the crank-pulley have to be heated to remove the crank bolt.

if you have the bolt out already you can use two short pry bars one each side of pulley and pry
evenly. it should slide off. If not you can use a big 2 jar puller. If you don't have the bolt out you can use a air impact or use a change wrench to hold pulley while you loosen the bolt with a long 1/2 inch ratchet. It is a 19 mm head bolt.

IF YOUR ENGINE IS A 3.0 V6 3VZ-E YOU REMOVE AIR INTAKE PIENUM,AND ALL SURROUNDING COMPONENTS REMOVE THE FUEL RAIL THE INJECTORS ATTACHED ,REMOVE INTAKE MANIFOLD,THEN YOUR EXHAUST CROSSOVER PIPE,EXHAUST MANIFOLDS REMOVE ALL BELT'S AND PULLEYS ,TIMING COVER .....BEFORE REMOVING YOUR CRANSHAFT PULLEY ,ALIGNMENT YOUR TIMING MARKS ,ON CAMSHAFT TIMING PULLEY LT,RT ,CRANKSHAFT TIMING PULLEY,THEN REMOVE TIMING BELT TENSIONER ,REMOVE ALL CAM SHAFTPULLEY'S AND CRANKSFT . REMOVE DISTRIBUTOR.REMOVE HEADCOVERS,CAMSHAFT,THEN YOU COULD GET TO THE HEAD BOLTS.