What is the maximum baudrate of the USARTs on the STM32G441 series?

Did you have a look in the data sheet in chapter 6 USART interface characteristics?

E.g.  stm32g441cb.pdf, Chapter 5 , p 162, USART interface characteristics

The USART interface characteristics in chapter 5 of stm32g441.pdf only mention the maximum speed that can be handled by the I/O pins. I found some more information on the USART baudrates in asynchronous mode in chapter 36 (page 1546) of RM0440. Although, this still does not give a simple answer. Assuming 8x oversampling and not using a prescaler, the highest achievable baudrate would be 170 Mhz / 8 = 21.25 MHz - which is about the maximum speed that the I/O pins can handle. I just need 1.5 Mbps, so that should not be a problem. However, when using fractional division to obtain a baudrate, the tolerance on the generated baudrate becomes quite high (3%). That is too much for mainstream applications (1%) and certainly too much for professional applications (< 0.3%). That is something to keep in mind. Since I also need USB, I am thinking about setting SYSCLK to 144 MHz, which is 12 * 12 MHz and 96 * 1.5 MHz. That should give me precise baudrates on USB and on the USART.