The Sedevacantist Catholic teachings and perspective I grew up in actually prepared me very well for pursuing a radical change in my biblical understanding and pursuit of truth.
For definition Sedevacantist translates to 'vacant seat'. We didn't believed the modern popes, since the 1950's, where actually popes. And did not follow any changes made in the church teachings with Vatican ll and after. So Latin Mass was still followed, etc. We also believed the church had been infiltrated by modernist Marxists. We didn't follow mainstream Catholicism at all. This infiltration had been happening for decades but all the cards fell into place and everything came into the open and changed with the Second Vatican council as the infiltration was complete. I now have the perspective the changes since Yeshua happened SO much earlier, ie by Constantine and with the stage being set for that infiltration the few hundred years leading up to it from the time of Yeshua. The enemy is always looking to corrupt from within.
I had a very strong personal belief in my faith as a child and young adult. I studied the beliefs, lives of the saints, doctrines, and history of the church and world( From the Catholic perspective) voraciously. It all made sense from the lens of following the church, popes, councils, and traditions that everything built upon. We read from the scriptures, but not from an actual bible. Outside of maybe the new testament, always with the interpretation of the church fathers. Scripture was assigned to Sundays on an annual cycle and you didn't really read outside of that. The gospels, epistles, revelation, psalms and old testament prophets that spoke of the Messiah were pretty much all. No Old testament outside of knowing the basic stories of the patriarchs and some of the more notable characters, Abraham, Issac, Jacob, Moses, Noah, Daniel, David, and the like.
We kept our Sunday sabbath religiously. Yes, Mass was essential. But also no servile work or commerce. Other Sacraments like Confession and Communion were also an integral part of regular observance.
My perspective now is that there are biblical truths and morality that the Catholic church built upon. As no religion can last without some truth. Outside of the changes noted in the 2nd and 4th commandments the others were strictly observed.
Some benefits I would say I received from my upbringing:
A solid grounding in the commandments and morality.
An understanding of the set apart aspect of Sabbath and desire to set aside the day for YHVH.
The ability and willingness to live a life going against the flow and easy path (From being part of a radical branch of Catholic)
A desire to search for and understand the truth, even if it meant I was on my own doing so.
Once I started diving into the bible, a desire to live my life and adapt my understanding to how YHVH and Yeshua laid out for right living.
I didn't jump right from Catholicism to Torah Keeping as I had my stint out in the agnostic secular and non religious world for some years in between. But I did have the morality of my childhood to ground my life and character and it is why I am where I am now.
I could go on, but I'll leave off with the thought that there are many sincerely believing people in the Catholic church who are following the false teachings, fences, and additions it brings. While at the same time they have these nuggets of biblical belief they hold onto as well because of the integration. So I pray that those seeds are the ones that can sprout in my family and other sincere believers.