My note about the S7 / S/ Edge was only made because you wrote about the S7 and then the S7 Edge in your opening post.
Even if it sounds annoying - the success is worth the small effort: First create a clean starting point with Stock Android. Flashing with Heimdall (Linux PC) or Odin3 (Windows PC) not only deletes or overwrites data, but also reformats all partitions and completely reinstalls the software.
Now you can replace the Android recovery on TWRP Recovery and install the CustomROM. With this procedure I have already completely revived Galaxys that I thought were dead.
By the way: TWRP with TWRP update is possible without further - nevertheless, I prefer the installation via Odin3/Heimdall for Galaxy Phones.
If you want to treblezies your S7/S7Edge, I’ll help you with that. But also GSI ROM need a clean starting base. Therefore - see above …:))
Besides: The S7 / S7 Edge surprisingly received another update from Samsung in September 2020. All previous versions have failed, only with this StockROM I could help an already sorted out to electronic scrap S7 Edge to new life.