Excerpt from my Qt5.15.2 app's snapcraft file in case it helps anyone

snapcraft.yaml

name: focus-project  # you probably want to 'snapcraft register <name>'
base: core18 # the base snap is the execution environment for this snap
version: '0.2.3-preview' # just for humans, typically '1.2+git' or '1.3.2'
summary: Your Kanban board even closer! # 79 char long summary
[...]
grade: devel # must be 'stable' to release into candidate/stable channels
confinement: strict

apps:
  focus-project:
    command: bin/focus_project
    autostart: focus-project.desktop
    extensions:
      - kde-neon
    plugs:
      - system-observe
      - opengl
      - network
      - network-bind
      - network-control
      - password-manager-service
      - unity7

parts:
  bin:
    source: bin/
    plugin: dump
    organize:
      '*': bin/