For example this is the code in question (inside mdb-form-control):

    <input [mdbValidate]="true" mdbInput id="tabLabel" name="tabLabel" formControlName="tabLabel" type="text" required class="form-control">
    <label mdbLabel for="tabLabel" class="form-label">Label</label>
    <mdb-error *ngIf="(tabLabel?.invalid && (tabLabel?.dirty || tabLabel?.touched))">Label is required</mdb-error>
    <mdb-success *ngIf="tabLabel?.valid && (tabLabel?.dirty || tabLabel?.touched)">Looks good!</mdb-success>

I had to change mdbValidate to [mdbValidate]="true" as shown above

My tsconfig.json is just the default but included below:

{
    "compileOnSave": false,
    "compilerOptions": {
        "baseUrl": "./",
        "outDir": "./dist/out-tsc",
        "forceConsistentCasingInFileNames": true,
        "strict": true,
        "noImplicitReturns": true,
        "noFallthroughCasesInSwitch": true,
        "sourceMap": true,
        "declaration": false,
        "downlevelIteration": true,
        "experimentalDecorators": true,
        "moduleResolution": "node",
        "importHelpers": true,
        "target": "es2017",
        "module": "es2020",
        "lib": [
            "es2018",
            "dom"
        ]
    },
    "angularCompilerOptions": {
        "enableI18nLegacyMessageIdFormat": false,
        "strictInjectionParameters": true,
        "strictInputAccessModifiers": true,
        "strictTemplates": true
    }
}

I can confirm I am experiencing the same thing.

I was just about to submit a question myself.

Error: Type 'string' is not assignable to type 'boolean'.

As a result I tried using it like this: [mdbValidate]="true" -- it is functional but it makes my input needlessly tall.

I subsequently had to disable this scss rule:

 .form-control.validate-success, .form-control.validate-error {
    /* margin-bottom: 1rem; */
}

Now it is working as intended.

Either there is something wrong with the Module (and/or Directive) or you need to update the documentation.