That is why Biological weapon of mass destruction is a great solution. (Not just for Türkiye, but also for other similar countries that want avoid all political and economic repercussions of making nukes yet need to posses deterrence) You can develop it in a lab with a handful of mid tier scientists. Something that is practically concealable from today's intelligence, unlike a nuclear WMD program. Which requires billions of dollars and over thousand people to develop the whole thing. (Multiple enrichment plants, development of delivery systems, production of sufficient numbers of warheads, force design, command and control, second strike capability) All of this is not practically concealable in 21th century. Or even wasn’t in 20th century.
On the other hand, the cost of a biological weapon is estimated to be about 0.05 percent the cost of a conventional weapon in order to produce similar numbers of mass casualties per kilometer square.
Moreover, their production is very easy as common technology can be used to produce biological warfare agents, like that used in production of vaccines, foods, spray devices, beverages and antibiotics.
Biological warfare - Wikipedia https://en.m.wikipedia.org/wiki/Biological_warfare
While, biological WMD doesn't have tactical battlefield usefulness, it can definitely serve as strategic deterrence. Even though USA can shoot down limited numbers of ICBMs carrying thermonuclear payload, it simply cannot shoot down virus.
In today's highly globalised And interconnected world (Unprecedented in human history) any decent intelligence agency has the ability to introduce multiple deadly viruses into enemy's territory that could conceivably result in large numbers of civilian casualties and cause severe disruption to economic and societal infrastructure, before the enemy catches up to one of the viruses with development, sufficient production and distribution of vaccine in time, let alone all of them.
And you don’t even have to declare to world that you posses biological WMD and have sufficient delivery system in place (which is far more easier than building ICBM and SSBN) for deterrence effect.
All you have to do during any crisis is to let your nuclear armed adversary know that you have biological WMD and the sufficient means to deliver it. Again, they don’t have to fully believe your threat. The very ambiguity will provide a level of deterrence that you wouldn’t otherwise have. More like how Israel's nuclear ambiguity work. To any sane adversary, taking such huge risk would be deemed unacceptable.