The error occurs due to a version conflict between eslint package versions between different dependencies.

admin@:~/projects/nodebb$ ./nodebb build
Dependencies outdated or not yet installed.
Installing them now...

npm error code ERESOLVE
npm error ERESOLVE could not resolve
npm error
npm error While resolving: nodebb@4.3.0
npm error Found: eslint@8.57.1
npm error node_modules/eslint
npm error   peer eslint@"^6.0.0 || ^7.0.0 || >=8.0.0" from @eslint-community/eslint-utils@4.4.0
npm error   node_modules/@eslint-community/eslint-utils
npm error     @eslint-community/eslint-utils@"^4.2.0" from eslint@8.57.1
npm error     @eslint-community/eslint-utils@"^4.2.0" from eslint@9.18.0
npm error     node_modules/nodebb-plugin-sso-oauth2-multiple/node_modules/eslint
npm error       eslint@"9.x" from nodebb-plugin-sso-oauth2-multiple@1.4.2
npm error       node_modules/nodebb-plugin-sso-oauth2-multiple
npm error         nodebb-plugin-sso-oauth2-multiple@"^1.4.2" from the root project
npm error   peer eslint@"^7.32.0 || ^8.2.0" from eslint-config-airbnb-base@15.0.0
npm error   node_modules/eslint-config-airbnb-base
npm error     eslint-config-airbnb-base@"15.0.0" from eslint-config-nodebb@0.2.1
npm error     node_modules/eslint-config-nodebb
npm error       dev eslint-config-nodebb@"1.1.4" from the root project
npm error   3 more (eslint-config-nodebb, eslint-plugin-import, nodebb-plugin-2factor)
npm error
npm error Could not resolve dependency:
npm error dev @stylistic/eslint-plugin-js@"4.2.0" from the root project
npm error
npm error Conflicting peer dependency: eslint@9.26.0
npm error node_modules/eslint
npm error   peer eslint@">=9.0.0" from @stylistic/eslint-plugin-js@4.2.0
npm error   node_modules/@stylistic/eslint-plugin-js
npm error     dev @stylistic/eslint-plugin-js@"4.2.0" from the root project
npm error
npm error Fix the upstream dependency conflict, or retry
npm error this command with --force or --legacy-peer-deps
npm error to accept an incorrect (and potentially broken) dependency resolution.
npm error
npm error
npm error For a full report see:
npm error /home/admin/.npm/_logs/2025-05-05T09_37_06_860Z-eresolve-report.txt

npm error A complete log of this run can be found in: /home/admin/.npm/_logs/2025-05-05T09_37_06_860Z-debug-0.log
Error installing dependencies!
message: Command failed: npm install --omit=dev
stdout: null
stderr: null
/home/admin/projects/nodebb/src/cli/package-install.js:138
                throw e;
                ^

Error: Command failed: npm install --omit=dev
    at genericNodeError (node:internal/errors:983:15)
    at wrappedFn (node:internal/errors:537:14)
    at checkExecSyncError (node:child_process:889:11)
    at Object.execSync (node:child_process:961:15)
    at pkgInstall.installAll (/home/admin/projects/nodebb/src/cli/package-install.js:129:9)
    at Object. (/home/admin/projects/nodebb/src/cli/index.js:50:18)
    at Module._compile (node:internal/modules/cjs/loader:1434:14)
    at Module._extensions..js (node:internal/modules/cjs/loader:1518:10)
    at Module.load (node:internal/modules/cjs/loader:1249:32)
    at Module._load (node:internal/modules/cjs/loader:1065:12) {
  status: 1,
  signal: null,
  output: [ null, null, null ],
  pid: 295719,
  stdout: null,
  stderr: null
}

Node.js v22.2.0

Found a solution - this will temporarily disable strict checking of peerDependencies:

npm install --omit=dev --legacy-peer-deps
./nodebb build