So here’s the code for my pushbutton

void PB_Init(void){
    RCC->AHB1ENR |= RCC_AHB1ENR_GPIOCEN;
    GPIOC->MODER |= ( 0x0 << GPIO_MODER_MODE13_Pos);
    GPIOC->PUPDR |= ( 0x1 << GPIO_PUPDR_PUPD13_Pos);
}

void EXTI15_10_Init(void){
    PB_Init(); // Initialize PC13 as input.

    RCC->APB2ENR |= (1<<14);      // Enable System configuration controller
    SYSCFG->EXTICR[3] &= ~(1<<7); // Select Port C as source, EXTIx = 0b0010
    SYSCFG->EXTICR[3] &= ~(1<<6); // Select Port C as source, EXTIx = 0b0010
    SYSCFG->EXTICR[3] |= (1<<5);  // Select Port C as source, EXTIx = 0b0010
    SYSCFG->EXTICR[3] &= ~(1<<4); // Select Port C as source, EXTIx = 0b0010
    EXTI->IMR |= (1<<13);         // Disable interrupt request mask on EXTI line 13
    EXTI->FTSR |= (1<<13);        // Enable EXTI on Falling edge
    EXTI->RTSR &= ~(1<<13);       // Disable EXTI on Rising edge
    RCC->APB2ENR &= ~(1<<14);     // Disable System configuration controller
}
volatile bool flag=0;
void EXTI15_10_IRQHandler(void){
    if(flag==0){
    TIM2->CR1|=TIM_CR1_CEN;
    flag=!flag;
    EXTI->PR |= (1<<13);  // Clear PR to re-enable EXTI interrupt

    }else{
        TIM2->CR1&=~TIM_CR1_CEN;
        flag=!flag;
        EXTI->PR |= (1<<13);  // Clear PR to re-enable EXTI interrupt
    }

}


void Interrupt_Init(void){
    EXTI15_10_Init(); // Step 1, this is defined elsewhere
    NVIC->IP[EXTI15_10_IRQn] =  (1 << 4);    // Step 3: Set priority to 1
    NVIC->ISER[40 >> 5] |= (1 << (40 % 32)); // Step 4: Enable interrupt
}

The issue with it is that whenever I push the button, my timer doesnt pause, it behaves randomly, goes to maximum-minimum, you never know. Never truly pauses

Tried messing with the flags and such, but to no avail