I recently managed to "hard-brick" my Motorola one 5g ace after updating magisk, getting stuck in a bootloop, and naively deciding to attempt to boot from the B slot instead. On qualcomm-based devices you can get into EDL (Emergency DownLoad) mode where you have nothing that is actually bootable on the device, and the phone will remain entirely unresponsive save for appearing as a serial device when plugged in over USB. You then need to "talk" to the phone with the appropriate protocol (Sahara or Firehose depending on the age of the device) and you can gradually work towards recovery. In my case I was able to manually reconstruct a valid bootloader.img for my particular software version, re-flash it, and get back into a "soft-brick" state from there.
However, I do know of some slightly older HTC devices that would have the EEPROM straight-up completely die, leaving the device permanently trapped in a "hard-brick" state unless someone felt like doing some BGA soldering.
Modern phones do have a lot of stuff running under the hood that makes it a lot harder to mess things up, but once you go off the beaten path things become much less certain.
