Had been using this app. for a long time but have switched to a more effective permission manager after noticing that App Ops was no longer working on certain apps., for me.

May I know which app?

Sure . . . it`s XPrivacyLua (Spoiler Alert — it`s an Xposed module.)

XPrivacyLua is no longer supported.

... use this open source alternative:
https://github.com/MuntashirAkon/AppManager/releases

Enticing features coming in the next/future update:

APK editing
Code editor
Routine operations
Finder: Find app components, permissions etc. in all apps
Enable/disable app actions such as launch on boot
Panic responder for Ripple
Crash monitor
Systemless disabling/uninstalling of the system apps
Import app list exported by App Manager
More advance terminal emulator
File manager
Database viewer and editor, etc.

May I know which app?

Sure . . . it`s XPrivacyLua (Spoiler Alert — it`s an Xposed module.)

XPrivacyLua is no longer supported.

Despite of which . . . it is effective — can you maintain the full functionality of Truecaller after blocking it from uploading your contacts to their servers with . . . any other permission manager?

.....maintain the full functionality of Truecaller after blocking it from uploading your contacts to their servers....

I'd like to know how this can be done. Care to write? Or, do you know of a how-to somewhere?

.....maintain the full functionality of Truecaller after blocking it from uploading your contacts to their servers....

I'd like to know how this can be done. Care to write? Or, do you know of a how-to somewhere?

Sure . . . here are my XPrivacyLua settings for Truecaller:—