Similar question.

Question

Ta télé est bien. 
télé is a noun, why not say "ta télé est bonne"?

Accepted Answer

Hi Rene,
Technically in this example, 'ta télé est bien' is correct as 'bien' follows the verb 'to be' and therefore is correct.
You wouldn't say 'ta télé est bonne' but you might say: 'C'est une bonne télé'.
Hope this helps!

Answer

Here is the explanation from the lesson:
«When to use bien (adverb) and therefore mieux
In French, you'll use the adverb bien and its comparative mieux when:
- making a general statement with être about something or someone being fine/OK/better/the best: 
Example:  Ta télé est bien mais la mienne est mieux. -->  Your TV is fine but mine is better.

I hope that helps.

Answer

Knowing when to use bien and when to use bon canbe confusion sometimes. With verbs that describe a state of being such as "être" the use of "bien" is favored. It wouldn't be entirely wrong to use "bon" but it means something different:

La télé is bien. -- The TV is good.
La télé est bonne. The TV is a good one.

-- Chris.

P.S.: Laura on her site has a valuable lesson on that:
https://www.lawlessfrench.com/grammar/bon-vs-bien/

Answer

Hmmm...In all my years of French language learning I never learned that "bien" rather than "bon" must follow être.

Answer

It is not a must. C'est bon is also correct but carries a slightly different meaning. In the example of the tv, la télé est bonne, however, does sound weird.
-- Chris.