SMART string for alkyl group excluding alcohols
How to find carbon

with four connections
not -CH3
and only connected to carbon

As in your SMILES there are only implicit hydrogen, you do not need to count Hs.
Count the explicit bonds and exclude the carbon with one explicit bond to avoid -CH3.
[CX4;D2,D3,D4]
To find the carbons that are connected to others than carbon
C[!C]
Now you can use recursive SMARTS, and set the second pattern to NOT.
[CX4;D2,D3,D4;!$(C[!C])]
Now only carbons would be found that match both patterns.
CX4   C with total connections of 4
D&lt;n&gt;  number of explicit bonds
$()   recursive SMARTS
!     NOT
;     AND
,     OR
In cyclohexanol it will find

and here is a dummy molecule for testing it.
CCC(F)C=CCC1CCC(O)C(C(C)(C)C)C1