Yes, it is certainly true, but to a point : The TLFi classifies the meanings into two parts;

I. Emplois vieillis, littér. ou figés.
A. Emploi trans.
B. Emplois trans. ind. Approcher de…

II. Emplois vivants
A. Emploi pronom. S’approcher de…
B. Emploi intrans. Approcher.

However, as it can be seen from the categories, “approcher” as an intransitive verb is still quite current; although a preference is apparently given to the pronominal verb in the spoken language (personal impression) this ngram shows that in print the intransitive verb is sometimes used more frequently: “approcha de sa”, “… de son”, “…de cette”.

There is no subtle difference as far as I can tell; the meaning is the same; I can impute this replacement to nothing else than the vagaries of usage.

For instance, from the two following possibilities only the second is correct (sense and usualness) (correction due to user jlliagre, see comments);

• Après avoir approché du bureau il y a posé un livre.
• Après s’être approché du bureau il y a posé un livre.

The verb approcher can be used a reflexive way and means that the subject gets closer to the object.

Je m’approche de la fenêtre. (I’m getting near the window.)

The opposite is:

Je m’éloigne de la fenêtre.

While the same sentence might have been used a non reflexive way in the past, you don’t really say in modern French (at least in France but it seems to sound odd in Canadian French too):

J’approche la fenêtre.

or

J’approche de la fenêtre.

These forms might be possible when approcher means to move something near something else, in which case the reflexive form is not possible, e.g.:

J’approche la chaise de la table (or better: je rapproche la chaise de la table) I move the chair toward the table.

The opposite is:

J’éloigne/écarte la chaise de la table

There are a few cases where approcher (de) is equivalent to s’approcher de:

Il approche la cinquantaine. (he is approaching his fifties)

Il approche de la cinquantaine.

Il s’approche de la cinquantaine.

Some where there is a nuance:

Il approche son client. He approaches his customer (The approach is deliberate and likely the first step of a plan).

Il se rapproche de son client. (He is getting closer physically or emotionally. That might not be deliberate.)

L’avion approche de Paris. (meaning L’avion est en approche de Paris. Its pilot is preparing the landing procedure)

L’avion se rapproche de Paris. (The plane is getting closer to Paris location but that might not be its actual destination.)

Some other where the reflexive form is unused:

Il approche le problème sous divers angles (also il aborde le problème…)

Il s’approche du problème sous divers angles.

See also "approcher" ou "s'approcher"