TS1086: An accessor cannot be declared in ambient context

Setting "skipLibCheck": true in tsconfig.json solved my problem

"compilerOptions": {
    "skipLibCheck": true
}

I had this same issue, and these 2 commands saved my life. My underlying problem is that I am always messing up with global install and local install. Maybe you are facing a similar issue, and hopefully running these commands will solve your problem too.

ng update --next @angular/cli --force
npm install typescript@latest

If it's just a library that's causing this, this will avoid the problem just fine. Typescript can be a pain on the neck sometimes so set this value on your tsconfig.json file.

"compilerOptions": {
    "skipLibCheck": true
}

I got the same issue when adding @angular/flex-layout to my Angular 8 project now with

`npm install @angular/flex-layout --save`.

This since now that command installed the major 9th version of the flex-layout package. Instead of upgrading everything else to the last version, I solved it by installing the last 8th major version of the package instead.

 npm install @angular/[email protected] --save

Quick solution: Update package.json

"devDependencies": {
   ...
   "typescript": "~3.7.4",
 }

In tsconfig.json

{
    ...,
    "angularCompilerOptions": {
       ...,
       "disableTypeScriptVersionCheck": true
    }
}

then remove node_modules folder and reinstall with

npm install

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