Hello, When sending data with UART, why can the UART data transmission process stop or be interrupted when an EXTI interrupt occurs?

Because you block in the IRQ Handler or callback routines. ie use delays or other spin loops, or blocking HAL functions.​

Hello,

i am new at this job.

I still couldn't get it to work.

EXTI, UART not working.

"couldn't get it to work" doesn't tell us much. You don't show us code for EXTI, and I don't see code to configure the GPIO pins for the UART. What happened when you ran the code above? Read back the UART and GPIO registers to see if they are configured as you expect. Did you look at the TX pin with a scope or logic analyzer? Did it do anything?

"USART1->CR1 |= 0x00" <---- Why is that there? This does nothing.

Post all of your relevant code. And please do not post PICTURES of your code. Copy/paste your code directly into you forum post using the "code" button "</>".