Many people didn’t even notice. Since the new Buddy Board was released with the new Prusa 3D printers, it was no longer possible to flash these boards with custom firmware without voiding the warranty.

This affected the Prusa MK3.5, MK3.9, MK4, and the Prusa XL. Fortunately, Prusa has changed its mind, and now the broken seal no longer voids the warranty. Thanks Prusa <3

You can find out more about breaking the seal and flashing custom firmware here: https://help.prusa3d.com/article/flashing-custom-firmware-core-one-mk4-s-mk3-9-s-mk3-5-s_814967

Third-party manufacturers can now also offer custom firmware for their upgrade products again. My Prusa MK3.5 with the Bondtech LGX upgrade, in particular, would be delighted with customized firmware. However, it’s unclear whether Bondtech will even offer this.