System:
    OS: macOS 11.6
    CPU: (12) x64 Intel(R) Core(TM) i7-8850H CPU @ 2.60GHz
  Binaries:
    Node: 16.13.1 - ~/.nvm/versions/node/v16.13.1/bin/node
    Yarn: 1.22.0 - /usr/local/bin/yarn
    npm: 8.1.2 - ~/.nvm/versions/node/v16.13.1/bin/npm
  Browsers:
    Chrome: 96.0.4664.93
    Edge: 96.0.1054.43
    Firefox: 92.0
    Safari: 15.1
  npmPackages:
    @ionic/vue: ^5.4.0 => 5.9.2 
    @ionic/vue-router: ^5.4.0 => 5.9.2 
    @vue/babel-helper-vue-jsx-merge-props:  1.2.1 
    @vue/babel-helper-vue-transform-on:  1.0.2 
    @vue/babel-plugin-jsx:  1.1.1 
    @vue/babel-plugin-transform-vue-jsx:  1.2.1 
    @vue/babel-preset-app:  4.5.15 
    @vue/babel-preset-jsx:  1.2.4 
    @vue/babel-sugar-composition-api-inject-h:  1.2.1 
    @vue/babel-sugar-composition-api-render-instance:  1.2.4 
    @vue/babel-sugar-functional-vue:  1.2.2 
    @vue/babel-sugar-inject-h:  1.2.2 
    @vue/babel-sugar-v-model:  1.2.3 
    @vue/babel-sugar-v-on:  1.2.3 
    @vue/cli-overlay:  4.5.15 
    @vue/cli-plugin-babel: ~4.5.0 => 4.5.15 
    @vue/cli-plugin-e2e-cypress: ~4.5.0 => 4.5.15 
    @vue/cli-plugin-eslint: ~4.5.0 => 4.5.15 
    @vue/cli-plugin-router: ~4.5.0 => 4.5.15 
    @vue/cli-plugin-typescript: ~4.5.0 => 4.5.15 
    @vue/cli-plugin-unit-jest: ~4.5.0 => 4.5.15 
    @vue/cli-plugin-vuex:  4.5.15 
    @vue/cli-service: ~4.5.0 => 4.5.15 
    @vue/cli-shared-utils:  4.5.15 
    @vue/compiler-core:  3.2.24 
    @vue/compiler-dom:  3.2.24 
    @vue/compiler-sfc: ^3.0.0-0 => 3.2.24 
    @vue/compiler-ssr:  3.2.24 
    @vue/component-compiler-utils:  3.3.0 
    @vue/devtools-api:  6.0.0-beta.20.1 
    @vue/eslint-config-typescript: ^5.0.2 => 5.1.0 
    @vue/preload-webpack-plugin:  1.1.2 
    @vue/reactivity:  3.2.24 
    @vue/ref-transform:  3.2.24 
    @vue/runtime-core:  3.2.24 
    @vue/runtime-dom:  3.2.24 
    @vue/server-renderer:  3.2.24 
    @vue/shared:  3.2.24 
    @vue/test-utils: ^2.0.0-0 => 2.0.0-rc.17 
    @vue/web-component-wrapper:  1.3.0 
    eslint-plugin-vue: ^7.0.0-0 => 7.20.0 
    jest-serializer-vue:  2.0.2 
    typescript: ^4.3.5 => 4.5.2 
    vue: ^3.2.1 => 3.2.24 (2.6.14)
    vue-eslint-parser:  7.11.0 
    vue-hot-reload-api:  2.3.4 
    vue-jest: ^5.0.0-0 => 5.0.0-alpha.10 (3.0.7)
    vue-loader:  15.9.8 (16.8.3)
    vue-router: ^4.0.0-0 => 4.0.12 
    vue-style-loader:  4.1.3 
    vue-template-compiler:  2.6.14 
    vue-template-es2015-compiler:  1.9.1

npm install -g @ionic/cli
npm install -g @vue/cli@next
ionic start --type=vue (pick blank project. call it vue-test)
cd vue-test
vue upgrade --next

% vue upgrade --next    
✔  Gathering package information...
  Name                         Installed       Wanted          Latest          Command to upgrade
  @vue/cli-service             4.5.15          4.5.15          5.0.0-rc.1      vue upgrade @vue/cli-service --next
  @vue/cli-plugin-babel        4.5.15          4.5.15          5.0.0-rc.1      vue upgrade @vue/cli-plugin-babel --next
  @vue/cli-plugin-e2e-cypress  4.5.15          4.5.15          5.0.0-rc.1      vue upgrade @vue/cli-plugin-e2e-cypress --next
  @vue/cli-plugin-eslint       4.5.15          4.5.15          5.0.0-rc.1      vue upgrade @vue/cli-plugin-eslint --next
  @vue/cli-plugin-router       4.5.15          4.5.15          5.0.0-rc.1      vue upgrade @vue/cli-plugin-router --next
  @vue/cli-plugin-typescript   4.5.15          4.5.15          5.0.0-rc.1      vue upgrade @vue/cli-plugin-typescript --next
  @vue/cli-plugin-unit-jest    4.5.15          4.5.15          5.0.0-rc.1      vue upgrade @vue/cli-plugin-unit-jest --next
? Continue to upgrade these plugins? Yes
Upgrading @vue/cli-service from 4.5.15 to 5.0.0-rc.1
npm ERR! code ERESOLVE
npm ERR! ERESOLVE unable to resolve dependency tree
npm ERR! 
npm ERR! While resolving: vue-test@0.0.1
npm ERR! Found: @vue/cli-service@5.0.0-rc.1
npm ERR! node_modules/@vue/cli-service
npm ERR!   dev @vue/cli-service@"~5.0.0-rc.1" from the root project
npm ERR! 
npm ERR! Could not resolve dependency:
npm ERR! peer @vue/cli-service@"^3.0.0 || ^4.0.0-0" from @vue/cli-plugin-router@4.5.15
npm ERR! node_modules/@vue/cli-plugin-router
npm ERR!   dev @vue/cli-plugin-router@"~4.5.0" from the root project
npm ERR! 
npm ERR! Fix the upstream dependency conflict, or retry
npm ERR! this command with --force, or --legacy-peer-deps
npm ERR! to accept an incorrect (and potentially broken) dependency resolution.
npm ERR! 
npm ERR! See /Users/daviesd/.npm/eresolve-report.txt for a full report.

npm ERR! A complete log of this run can be found in:
npm ERR!     /Users/daviesd/.npm/_logs/2021-12-09T18_24_01_854Z-debug.log
 ERROR  Error: command failed: npm install --loglevel error @vue/cli-service@~5.0.0-rc.1
Error: command failed: npm install --loglevel error @vue/cli-service@~5.0.0-rc.1
    at ChildProcess.<anonymous> (/Users/daviesd/.nvm/versions/node/v16.13.1/lib/node_modules/@vue/cli/lib/util/executeCommand.js:138:16)
    at ChildProcess.emit (node:events:390:28)
    at maybeClose (node:internal/child_process:1064:16)
    at Process.ChildProcess._handle.onexit (node:internal/child_process:301:5)