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Does Bhagavad Gita say bhakti is best of all processes anywhere? If yes, does it say it is the only process for realizing god?

In the very last chapter of the Gita, God says(chapter 18, sloka 65):

Have your mind fixed on Me, be My devotee, be a sacrificer to Me and bow down to Me. (Thus) you will come to Me alone. (This) truth do I pormise to you. (For) you are dear to Me.(Translation by Swami Gambhirananda)

So having shown the different paths of Raja-yoga, Jnana-yoga, Karma-yoga and Bhakti-yoga to reach Him, He ultimately asks Arjuna to be His Devoee.

I think He makes Bhakti the top-most by this verse.

Depends on what you mean by "topmost"

I think he just says it is easier than attaining the formless God.

https://www.holy-bhagavad-gita.org/chapter/12

Bhagavad Gita 12.1
Arjun inquired: Between those who are steadfastly devoted to Your personal form and those who worship the formless Brahman, who do You consider to be more perfect in Yog?

Bhagavad Gita 12.2
The Blessed Lord said: Those who fix their minds on Me and always engage in My devotion with steadfast faith, I consider them to be the best yogis.

Bhagavad Gita 12.3 – 12.4
But those who worship the formless aspect of the Absolute Truth—the imperishable, the indefinable, the unmanifest, the all-pervading, the unthinkable, the unchanging, the eternal, and the immoveable—by restraining their senses and being even-minded everywhere, such persons, engaged in the welfare of all beings, also attain Me.

Bhagavad Gita 12.5
For those whose minds are attached to the unmanifest, the path of realization is full of tribulations. Worship of the unmanifest is exceedingly difficult for embodied beings.

Bhagavad Gita 12.6 – 12.7
But those who dedicate all their actions to Me, regarding Me as the Supreme goal, worshiping Me and meditating on Me with exclusive devotion, O Parth, I swiftly deliver them from the ocean of birth and death, for their consciousness is united with Me.

Krishna takes Arjuna through karma, jnana and bhakti yogas and gives him a choice in BG 18.63 to as he wishes.

But when it comes to the real solution, he mentions simply this in BG 18.66:

sarva-dharmān parityajya mām ekaḿ śaraṇaḿ vraja ahaḿ tvāḿ
sarva-pāpebhyo mokṣayiṣyāmi mā śucaḥ

Commentary by Sri Abhinavagupta of Kaula Tantra Sampradaya:

18.66 Sarvadharman etc. Abandoning all attributes : This act of slaying the kinsmen and the like that arises incidentally while
fighting a war – not owning those acts as your own attribute by your
thought ‘I am the doer of all these’; also giving up by mind, the
notion ‘If the act of slaying the teacher etc., is avoided, merit will
accrue to me’. come to Me: Come to Me alone, the Agent-of-all-actions,
the Supreme Lord, the Sovereign. As your Refuge : as the Guardian of
all your natural impulses. On that account I, the Omniscient, shall
rescue you from all the sins. Don’t be sorrowful : Don’t get perplexed
‘What to be done’.

It is very clear that he says Arjuna should surrender to him, not just be a devotee or not just as a friend. So, it is clear that sharanagati is either higher than bhakti yoga or it is the end result of bhakti yoga.

Even after saying that he is very clear that BG 18.71 that this message will help only those with faith and without Envy.

Krishna is also clear that surrendering to him, as a person, directly, is the easiest way as mentioned in BG 12.5

Commentary by Sri Abhinavagupta of Kaula Tantra Sampradaya:

12.3-5 Ye tu etc. upto avapyate. On the other hand, those, who contemplate on the Self as the motionless Brahman – by them also all
the attributes of Absolute Lord are superimposed on the Self – the
attributes that are indicated by the adjectives ‘omni-present’ etc.
Therefore even the contemplators of the [attributeless] Brahman reach
nothing but Me, of course. However, the trouble they undergo, is much
more. For, they [first] superimposed on the Self the actonary of
attributes like absence-of-sin etc., and then comtemplate on It. Thus,
while without any effort [on the part of the contemplator] the Lord is
readily available with the greatness due to the host of
self-accomplished attributes, these persons undergo two-fold trouble.