When I say "true" church, I speak of that which is told of in Acts 11

https://www.kingjamesbibleonline.org/Acts-Chapter-11/

The first thing you should look for, does the church believe that the Word of God is the final authority? No true church would hold councils, or issue edicts, etc. to correct or change the Word of God. Period.

Secondly, is the church using the Divinely Inspired Word of God or one of the versions that man has altered? A brief quote from wiki defining this

In textual criticism of the New Testament, the Byzantine text-type (also called Majority Text, Traditional Text, Ecclesiastical Text, Constantinopolitan Text, Antiochian Text, or Syrian Text) is one of the main text types. It is the form found in the largest number of surviving manuscripts of the Greek New Testament. The New Testament text of the Eastern Orthodox Church, the Patriarchal Text, as well as those utilized in the lectionaries, are based on this text-type. Whilst varying in at least 1,830 places,[1] it also underlies the Textus Receptus Greek text used for most Reformation-era (Protestant) translations of the New Testament into vernacular languages.

Modern translations (since 1900) mainly use Eclectic editions that conform more often to the Alexandrian text-type.

The basic summary to this is that Bible versions faithfully translated from the "Textus Receptus" are true versions, while those taken from the Alexandrian texts, such as the "B" or "Aleph" are not (these are not original manuscripts, they were "recreated" by man and are believed to have originated in Italy.)

Feel free to use the above information to do your own study of the matter.

Thirdly, does the church deny the power of the Holy Spirit to provide believers with a version of the Bible that is without error and easily understood by those who seek the Truth?

Fourthly, does the church literally interpret the Word of God? This may surprise some but many, if not all, of the post 100AD early church "fathers" would interpret the scriptures metaphorically and, in doing so, introduced errors and false doctrines. (A great example of this is that not one of the Apostles, in all of the New Testament, prayed to Mary. Nor do they cite any of the apochypha writings, but do quote, over 200 times, from the original 39 books of the Old Testament. Things such as these were brought in afterwards, in error.)

Fifthly, does the church "rightly divide" the Word of God, into Dispensational Ages? To simplify this without going off into a major discourse, does the church still preach against the eating of bacon? Or that salvation requires works?

Sixthly, is the church evangelistic, as told in Acts chapters 1 and 13. 1:8But ye shall receive power, after that the Holy Ghost is come upon you: and ye shall be witnesses unto me both in Jerusalem, and in all Judaea, and in Samaria, and unto the uttermost part of the earth.

Seventhly, do they properly define baptism? Acts 1:5 For John truly baptized with water; but ye shall be baptized with the Holy Ghost not many days hence. Again, dispensationalism.

There is more, much more, but this is a good start.