There are alternatives. Pushy is pretty easy to use, and it’s not that hard to allow it to run in the background. See: https://support.pushy.me/hc/en-us/articles/360043423332-How-can-I-send-notifications-to-Android-devices-in-Doze-power-saving-mode-

Of course, an OEM may do aggressive app killing where the above may not work (Huawei is notorious for this), but that is an OEM-specific issue that applies to all apps in general, so as a developer it’s up to you whether you want to test against, or even support such OEMs.