As of my last update, there is no official custom ROM available for the Oppo A5s. The issue you mentioned about not being able to uninstall the App Market even with ADB App Control is a common problem with some Oppo devices due to the ColorOS skin. Since there isn't much information on the XDA Forum regarding this specific phone model, it might be challenging to find a custom ROM or workaround for this issue.
However, there are some alternative methods you can try to disable or hide the App Market on your Oppo A5s. One possible solution is to use a third-party launcher that allows you to customize the app drawer and hide specific apps. Another option is to use a package disabler app from the Play Store to disable the App Market app without uninstalling it.
It's essential to proceed with caution when using third-party apps or methods to modify your device, as it can potentially void your warranty or cause other issues. If you're not comfortable with these methods, it's best to wait for an official solution from Oppo or the developer community.
I recommend keeping an eye on the XDA Forum and other developer communities for any updates or developments regarding custom ROMs or solutions for the Oppo A5s. Additionally, reaching out to Oppo's customer support for assistance with the App Market issue may also be beneficial.