Android OnePlus 3T stuck on boot logo, how can i recover data?
there is a 3rd way for locked bootloader without erasing userdata, but it all depends on the qualcomm factory loader firehose programmer which is special for each model  

these are expert tools for EDL mode to dump partitions or install TWRP from where you should be able to decrypt  

https://github.com/alephsecurity/firehorse  

https://github.com/bkerler/edl  

but i can't guide you i have no experience