The idea that there might be a single true religion among the literal thousands (arguably far more) that exist is problematic if we also take for granted that every single other is "false" in some meaningful way.
The nature of those problems will, of course, depend on what is understood by "true" religion, but here are some reasonable possibilities.
1. "True" may simply not mean much when used as a qualifier for religion. It makes sense in a way. How "true" can be something when constrasted with "false" specimens if the difference is hardly ever clear for most of humanity?
2. As noted above by myself and others, "true" religion may need to be defined on an individual level for the distinction to be meaningful. For some perspectives this is my favored take, although I would still choose better words instead of "true".
3. "True religion" may be treated instead as an alternate form of acknowledging that the idea of religion is generally too ill-defined to have any clear meaning. However, for that purpose it is unnecessarily loaded and confrontational wording. It would be IMO far better to simply develop better, more specific terminology.
4. Or we could instead go the other way around and be selective, accepting that so-called religions are too varied in nature and purpose and decide that we want to accept some and not others as proper and valid according to some criteria. A fine approach, but it too comes at a diplomatic cost and it may make for some difficult mutual undestanding. All the same, this is one of the most constructive approaches.