On the RP2040 this is solved by having a huge ground pad in the middle[1], as it has somewhat modest needs.
On modern CPUs there are tons of "redundant" ground pins sprinkled all over[2]. Just about every high-speed GPIO pin and power pin has it's own ground pin right next to it.
Keep in mind "high speed" mostly relates to having fast edges. You can have EMI issues with a "slow" 1MHz signal if the edges have rise/fall times are say a few ns, which modern microcontrollers can do.
On modern CPUs there are tons of "redundant" ground pins sprinkled all over[2]. Just about every high-speed GPIO pin and power pin has it's own ground pin right next to it.
Keep in mind "high speed" mostly relates to having fast edges. You can have EMI issues with a "slow" 1MHz signal if the edges have rise/fall times are say a few ns, which modern microcontrollers can do.
[1]: https://datasheets.raspberrypi.com/rp2040/rp2040-datasheet.p... (1.4.1)
[2]: https://en.wikichip.org/wiki/amd/packages/socket_am5#Pin_Map