Ukraine’s territorial integrity is nonnegotiable for Turkey, Erdoğan says

I don't think so. Turkiye has invested a lot in its military the past years and they are also heavily using it to fight Kurdish "terrorists" and establish "security buffer zones" in Syria. Also Turkiye while on difficult terms with the rest of NATO is controlling the Bosporus, which is vital for controlling the Black Sea. Russias Navy can easily be locked in in the Baltic and the Black Sea, which is why they were so eager to keep the Tartus base in Syria, as its only direct access to the Mediterranean Sea.

Finally for invading Turkiye Russia has to go through the Kapart Mountain range or along the coast through Turkiyes and Israels lapdog Azerbaijan and then Iran, or try a naval invasion from the Black Sea. Both are a logistical headaches.

So NATO is stronger on this flank, has a much stronger strategic interest and logistics are a pain. The other way round the Mountains and the Sea offer some cover, so Russia can defend on that flank. It makes more sense to go for the Baltic states next, if Russia wants to expand into this direction. Bonus points for having Ukraine and Belarus as a buffer zone to Poland and then Slovakia and Hungary as kind of Russian assets, further keeping that front safe.