One thing to remember is that there are differences among even the denominations - Southern Baptists are different from Free Will Baptists or Primitive Baptists, for example. This is something that many of my friends who were born and raised Catholic don’t understand.
For example, I can speak for myself. I was born and raised Protestant. At various points, I was Southern Baptist, evangelical non-denominational (which is not a denomination
per se, being more of a series of independent churches with little cohesive theology), and Reformed Presbyterian/Calvinist. Yes, there is a wide variety of theology within those groups. They do not agree with each other on some things, but they readily agree on others. Broad brushstrokes would not work here.
In the spirit of the OP, I can tell you various unScriptural beliefs I held and under which group I was taught what:
OSAS/Perseverance of the Saints - Southern Baptist, Evangelical Non-denominational, Reformed Presbyterian
Unconditional Election - Reformed Presbyterian; to lesser extent, Evangelical Non-denominational - this is the doctrine that God chooses an individual without any consideration of his/her merit and nothing we do can influence this
Total Depravity - Mainly Reformed Presbyterian, but all three have bits of this - This teaches that we are completely corrupted by sin and we are born again not of our own will but of God’s. You cannot choose God nor can you choose your own salvation because you are completely corrupt.
Limited Atonement - Reformed Presbyterian. Teaches that Jesus only died for the elect (the chosen).
Irresistable Grace - Mainly Reformed Presbyterian, although the Evangelical Non-Denominational had some of this - Teaches that you cannot resist God’s grace in your life. Once He calls you, you WILL be His child. Forever. And nothing will change that.
Sola Scriptura - All three, although the Reformed Presbyterian has a great devotion to the Westminster Confession of Faith, which was penned in 1646.
Sola Fide - All three.
Rapture, Tribulation (as described in Tim LaHaye’s works) - Evangelical Non-Denominational, Southern Baptist. My friends in the Reformed Presbyterian church were split on this; some were more in line with the Catholic understanding.
Each man/woman interprets Scripture with authority for himself/herself - All three, especially Evangelical Non-Denominational. Usually the priesthood of all believers is the justification for this.
Divorce and remarriage for any reason, at any time, no-fault - All three.
Women in church authority - Evangelical Non-Denominational. Specifically, female deacons.
All churches have truth, except the Catholic Church - Evangelical Non-Denominational. The other two would agree that the Catholic Church is not at all okay, but they would probably argue that they have the fullness of truth and not others.