The first half of the sentence which you have bolded is the answer, alongside what
@THX 1138 has explained.
Besides, given how the PLAN is going all-in with CATOBAR into the future WRT carrier procurement, it makes little sense for Shenyang AC to revert back to develop a STOBAR variant of the J-15B, when doing MLU onto the present J-15s and J-15As is the more cost and effort-effective option.
Same reason why Shenyang AC opted to drop J-11D in favor of upgrading J-11Bs to J-11BGs, plus introducing J-16s into the PLAAF - In conjunction with Chengdu AC's J-20 entering production.
So far, we still don't have any concrete information that the J-35s will also go onboard Liaoning and Shandong. So until then, I'd hold a "wait-&-see" attitude.
You still don’t get it. There is no technical reason why J-15B and J-35 can’t be launched from STOBAR carriers without modifications.
Both of you are jumping the gun a little bit.
The question about whether CATOBAR fighters can take off from STOBAR carriers (ski jumps), in the case of J-15B and J-35/XY, is something that has already been discussed and debated in the past and the outcome was (and still remains): inconclusive.
Fundamentally, we don't know the specific extent of airframe strengthening that is needed for a ski jump takeoff, and whether that would be already present for an aircraft designed to have fuselage reinforcement for CATOBAR takeoff and recovery (J-15B and J-35/XY), or whether there are other airframe stresses for a sustained ski jump takeoff independent of fuselage reinforcement needed for CATOBAR takeoff and recovery.
If a CATOBAR compatible fighter doesn't need additional reinforcement for ski jump takeoff, then great it will naturally allow cross deck operations between the PLAN's STOBAR carriers (CV-16, 17) and future CATOBAR carriers.
On the other hand, if a CATOBAR compatible fighter does need additional reinforcement for ski jump takeoff, the question becomes one of whether it would be worthwhile to have developed J-15B and J-35/XY from the outset to have that ski jump specific reinforcement in addition to its obvious CATOBAR reinforcement. The obvious major benefits being that you can crossdeck, the drawbacks being a likely minor weight penalty (but where even minor weight additions are meaningful).
Both of you have used somewhat strong, confident language, as below:
"The J-15B is the CATOBAR variant, hence they will
never serve onboard Liaoning and Shandong."
and
"There is
no reason why not"
Instead, it is most correct to say "at this stage we cannot say if J-15B and J-XY/35 will be compatible with regular STOBAR operations in addition to their known CATOBAR compatibility".