If you want to check beforehand (or afterwards), if your ROM supports Signature Spoofing, use this [tool](https://f-droid.org/de/packages/lanchon.sigspoof.checker/).
If your `/system/framework/services.jar` file contains the file `classes.dex`, you can skip deodexing and start patching right-away, else following theese instructions.
Android 9.0 is currently not supported by smali/baksmali (more precisly O/DEX format 039 and OAT format changes are not yet implemented).
VdexExtractor will create CompatDex for Android 9.0 (more precisely VDEX 019 files) instead of DEX. Theese CDEX files can only be manually converted to DEX on a GNU/Linux or MacOS PC, see [vdexExtractor: Strategy to convert CompactDex back to StandardDex](https://github.com/anestisb/vdexExtractor/issues/23)
If you can see `/system/framework/oat/[arch]/services.vdex`, where [arch] is the device architecture (arm, arm64, x86 or x86_64), you should follow theese instructions.
if it's properly been created rename it to classes.dex and add it to `services.jar`, if there are additional files like services.apk_classes2.dex, rename them to classes2.dex and so on and add them to services.jar like:
If you can see `/system/framework/oat/[arch]/services.odex`, where [arch] is the device architecture (arm, arm64, x86 or x86_64), you should follow theese instructions.