This is true, by default Android apps do not trust user-installed certificate authorities. IMO the easiest solution if you're doing security testing on a dedicated device is MagiskTrustUserCerts[1]. If you're not testing on a dedicated device or you don't want to root the device, I'd recommend using the objection[2] tool which has a guided mode for patching an apk, and you can modify the manifest to add your CA or to trust all user-installed CAs.
[1]: https://github.com/NVISOsecurity/MagiskTrustUserCerts
[2]: https://github.com/sensepost/objection/wiki/Patching-Android...