Thanks to Monk for the challenge.
Great fun! A few new words for me today. We have both Toscanini and Puccini on opposite sides of the grid (they apparently had a tempestuous friendship), but I don’t see more to it. The grid contains a pangram which is always a nice touch. Many thanks to Monk!

E.G.< (maybe, <retiring) + (SAGE (wise guy) on T (tense) + THEMES (subjects))
STEPS ON (moves against)
‘Issue’ meaning child in this context
CONE (solid object) securing SUM (whole)
Double definition
(TOXIN DATA IN)* (*aberrant)
LEAD IN (intro) before (QUOTING* (*rubbish) about E (English) + S (society))
JACK IN (ditch) + THE PULPIT (above which cloth may go)
EVER (at any time) in (A DISNEY)* (*complex)
CO2 (colourless, odourless gas) expanded
LOO (place to go) around (RE (on) + NZ (New Zealand))
A reference to Shakespeare’s Merchant of Venice perhaps?
[sop]ORIFIC E[legy] (section of)
OPPO (cohabitee) + (I INSTRUCT)* (*somehow)
ELECT (choose) + RA (artist)
TOSCA (opera) joining [me]N IN I[olanthe] (quartet of)
[st]ERN (rigorous, putting ST (good man, saint) down)
Max Ernst is a German artist of the Dada and Surrealist movements.
(RULES ONCE)* (*broken)
SIN (function) on AI (e.g. Claude)
Claude is one Artificial Intelligence application
Mount Sinai is biblical – the place where Moses received the ten commandments written on stone tablets
G (good) + AMI (friend, from French) catching OUR (setter’s and solvers’)
ASP (snake) with (LETHAL* (*bent) bites JUNG (psychologist))
Double definition
The second definition is self-explanatory, and the first British slang for male genitalia
STAGE* (*shifted) ahead of BOUT (fight?)
(IS NERVOUS)* (*criminal)
Australian dialect uses the word ‘souvenir’ as a verb meaning to steal something – usually something small
OVER (several deliveries, cricket) in CUP (container)
(IN + I (international) + C (clubs) + CUP (trophy))< (<being lifted)
RO[b] (nick, almost) keeps ONE (individual)
R (Republican) wearing DOWN (blue)
[16d … like the Lufthansa ashtray we have that somebody once souvenired from an airport lounge]
[Hmm, or the Finnair pillowcases by Marimekko]
24 That Lorenzo, certainly, or perhaps de Medici.
Liked JACK-IN-A-PULPIT, GET THE MESSAGE, ENCLOSURE and NEVER SAY DIE.
Undone by GOURAMI and RONEO, not having heard of either.
Thanks to Monk for the workout and Oriel for dishing up the necessary.