It's very likely that Ottoman soldiers couldn't break through the torso protection on late Medieval knightly armour, except with firearms (and the same applies to everybody else facing late Medieval knightly armour). However, there are gaps, and the arm and leg armour is much thinner (often under 1mm). Knights in plate armour are not invulnerable. Given the outcomes of battles like Kosovo (1389) and Nicopolis (1396), the Ottomans didn't have excessive difficulty killing knights on the battlefield, even before the arquebus/musket came into widespread use in their armours. Later, with their enemies better armoured, firearms were much more plentiful, and the better armour still didn't stop them from killing knights aplenty (e.g., Mohács (1526), and plenty of guns can be seen in https://commons.wikimedia.org/wiki/File:1526-Suleiman_the_Magnificent_and_the_Battle_of_Mohacs-Hunername-large.jpg which is a 16th century depiction of the battle).

This is not to dismiss the effectiveness of such armour. It worked. It just didn't work against everything. The Ottomans appreciated the value of armour, and make use of their own armoured cavalry and infantry:

• https://commons.wikimedia.org/wiki/File:Armors_for_Man_and_Horse,_Syrian,_Iranian_and_Turkish,_comprehensively_about_1450-1550,The_Metropolitan_Museum_of_Art,_New_York.jpg

• https://commons.wikimedia.org/wiki/File:Ottoman_Mamluk_horseman_circa_1550.jpg

• https://commons.wikimedia.org/wiki/File:MIA_-_Islamic_Knight.jpg

• https://commons.wikimedia.org/wiki/File:Ottoman_armour._Chain_armours_and_cuirass.jpg

Armour was not something they were new to facing.

As for Arab armour, there wasn't any qualitative difference between Crusader armour and Saracen armour during the Crusades in Syria/Palestine/Egypt, as I discussed in https://old.reddit.com/r/AskHistorians/comments/b6d6qn/a_common_view_during_the_crusades_is_that_the/

Some Arabs made very little use of armour. Joinville, in his Life of Saint Louis, wrote:

Another point is, that no man can die before his predetermined day. This the Bedouins so firmly believe, that they never go in armour to battle; for, if they did, they would think they were acting contrary to the dogmas of their faith. When they swear at their children, they usually say, "Mayest thou be cursed like him who arms himself for fear of death," which, they think, every one should be ashamed of.

However, many Arabs wore much armour, and fought as armoured cavalry.