In a lot of sentences lassen has the same grammar structure of modal verbs for example:
Kundenanfragen lassen sich schneller und effizienter bearbeiten.
If it’s a modal verb, when should we use it and for which situation?
I found a quite good explanation of the verb lassen here, but it is in German.
The essence is, lassen is a verb that can be used as a full verb, as a modal verb in different ways and even as a substitute for a passive form. Just to answer your question:
Dict.cc has several translations listed, similar to the previous link. From the previous I will try to translate some examples in the next passage.
Vollverb = nicht mehr tun: Ich lasse das Rauchen. (= Ich rauche nicht mehr.)
Full verb = stop doing sth: I quit smoking. (= I won’t smoke anymore.)
modalverbähnlich (1) = veranlassen: Ich lasse mein Fahrrad reparieren.
Similar to a modal verb (1) = cause/arrange sth.: I am having my bike repaired.
modalverbähnlich (2) = erlauben: Die Mutter lässt die Kinder bis spät in die Nacht fernsehen.
Similar to a modal verb (2) = allow: The mother allows her children to watch TV until late at night.
Passiversatzform sich lassen (3. Person) = können (+ Passiv): Das Auto lässt sich reparieren. (= Das Auto kann repariert werden.)
As substitute for a passive form (3rd person) = can (+ passive): ** (= The car can be repaired.)
** I do not know a literal translation here, that would not sound really queer.
The answer to the question in your title is a definite 'no'.
Yes, the grammatical structure is the same and certainly looks like it behaves like a modal verb, but in reality it doesn't feature the key characteristic, it doesn't express any modality, any sentiment of possibility or necessity. This is called linguistic modality (hence modal verb). More on that here and here is a short exerpt:
Modale Aussagen sind in diesem Sinn v. a. Aussagen über Möglichkeit oder Notwendigkeit
This is an important aspect, otherwise, a lot of verbs would also be considered modal when they really aren't, e.g.
gehen. You could use gehen in this manner:
So, ich gehe schlafen. Gute Nacht!
Same structure, no modality.
Lassen is a modal auxiliary from some perspective, as it can be used to express adhortative mood:
Lass uns gehen!
It's the same as "Let us go" and appears in most, if not all germanic languages (checked most of the contemporary germanic languages). Depending on how we define 'modal verb' - and the most conclusive definition would be 'auxiliary verb that can be used to express grammatical mood' - then it is actually a modal verb, although it is limited to a very specific use case.
Apart from that, mood is not just about necessity and possibility. It is a way for the speaker to "express their attitude towards what they are saying" (Wikipedia). There are realis moods referring to events that are factual and true, and therefore do not express necessity or possibility.
However, as far as I know, there is no German modal verb which can form any realis mood, but it is of course possible in theory.
Depending on how far you take the definition of auxiliary verb, 'lassen' is an auxiliary that can be used to construct causative, which is a form of diathesis.