As long as the microcontroller can program its own flash you can implement a bootloader.
The real question is: do you want to write your own (complete flexibility on the target device, the features, the protocol, the transport medium, the loader application) or not? (you can only use the target supported by who provides the bootloader, you are subjected to the features and limitations of who wrote the bootloader, you are restrained to the medium provided by who wrote the bootloader, you have to use the application written by who made the bootloader in case you can't customize it with your logo or whatever)
If you don't want to write your own, stick to whatever microchip offers, but then you'll probably need to move to a part that is unnecessarely big/complex, because they don't care about supporting every chip with their code generators.
But I've written plenty bootloaders myself using uart, USB (HID or Vendor, will have to do with CDC next month), LIN, CAN, for any possible target. It's just firmware, saying that PIC24 can't do USB loaders is laughable.
writing a bootloader is nothing special over any other part of the firmware, it just requires some design effort on your part, as with everything.
It's MCC that is a gigantic unredeemable piece of shit, the much older MLA which is based on did have USB bootloaders for PIC16, PIC18, PIC24. They just don't want to provide them anymore because having a graphical interface to generate every possible variation is HARD to do. According to MCC you can do USB CDC and HID, but not Audio or Vendor, as if there was something special about them (hah.)
Anyway: Most of our products are configured/updated using UART. However, of the thousands we send out every year, the actual customers that are required to update the configuration/firmware are very few. So we bought a lot of USB-TTL cables for 2€ each on aliexpress, changed the connector so it fits our programming interface and provide them to said customers. Fir even fewer exceptions, we do not send out firmware in alpha state and once the unit is installed it's very likely it is never touched again for years