This is my situation:
I had Acer E15 with win10 on an SSD and secondary empty HDD. I replaced the HDD with another SSD and re-installed win10 on the new SSD. Then I tried installing Ubuntu 18.04 on the original SSD to have dual boot. I followed this: Dual Boot Windows 10 and Linux Ubuntu on Separate Hard Drives
While doing the partitions I had an existing EFI partition on the original SSD which had label like "windows boot loader". I deleted that one thinking linux EFI would be good enough for the Grub menu to show and identifying both OS. It didn't work out and got the "no bootable device" message. I did re-install linux again but same problem. I did disable safe boot through installs. I used this to fix the no bootable device thing: https://itsfoss.com/no-bootable-device-found-ubuntu/ but still no grub menu. I updated grub as well and still don't have the dual boot. How can I do that? Is it possible at all at this point to have dual boot of the existing win10 and ubuntu?