Turkish

• https://www.degruyter.com/document/doi/10.1515/9783110220261.159/html "Mutual intelligibility is high between Turkish and Gagauz and also among the Kipchak languages." [tur]<>[gag] and [tur]<>[uzn]
• https://plc.sas.upenn.edu/turkish "Turkish is mutually intelligible, barring these vocabulary differences, with the Turkic languages spoken in adjacent areas, such as Azerbaijani, Uzbek, and Turkmen. A speaker of Turkish can be understood as far east as Kyrgyzstan."
• https://tehlikedekidiller.com/wp-content/uploads/MA_Robert_Lindsay_Mutua... "Turkish has about 65-90% intelligibility with Azeri. After a few weeks of close contact, they can often communicate pretty well." "Kazakh and Kirghiz are also close, with probably 75-80% intelligibility between them." "Tatar and Bashkir are probably even closer to that, with intelligibility on the order of 85%." "Uzbek and Uyghur are fairly close, but they are still probably only 65-70% intelligible." "Personally, I think the intelligibility of Turkmen and Turkish is probably around 40%. Turkish has low intelligibility between Crimean Tatar and Karaim. Crimean Tatar speakers say that Turks cannot understand their language." "The intelligibility of Turkish and South Azeri may be quite high, on the order of 85% or so, higher than between Turkish and North Azeri." "I would estimate that Turkish-Kazakh intelligibility is less than 40%." "Gagauz has very high intelligibility with Turkish, so high that it may be a dialect of Turkish."
• https://www.researchgate.net/publication/321875105_The_Effect_of_Typolog... A table with various figures
• https://www.academia.edu/4068771/Mutual_Intelligibility_Among_the_Turkic... page 9 there are various figures, for instance 67% between Turkish and Turkmen (based on a Swadesh-215 list with borrowings)
• https://www.turkceogretimi.com/dil-uezerine/the-internal-classification-... Another good source (without borrowings, Turkish and Turkmen at 73.6% for instance)
• https://www.researchgate.net/publication/341445391_A_Comparison_of_Moder... Another dataset

So there are various, and sometimes contradicting, claims. A big issue is the asymmetric intelligibility: Turkey is now the second biggest TV exporter in the world ( https://haymillian.com/turkish-delight-how-turkey-has-become-the-second-... ) so Turkic speakers from all around the world watch Turkish series and this has made the Istanbul accent more understandable. At the same time, Turkish power is growing and more and more Turkic speakers do business with Turkey, visit Turkey for tourism, go there to study or work, etc. So a young educated Azeri, Iraqi Turkmen, or Uzbek most likely understand Istanbul Turkish. The opposite may not be true.

"Turkish heritage speakers in Sweden constitute a sizeable minority, but are far from the largest immigrant minority in the country. As Swedish authorities are prohibited from collecting census data regarding ethnicity and speakers of a certain language, the exact number of Turkish speakers is unknown; our own estimate, based on Statistics Sweden (2017), is that there are ca 100,000 Turkish speakers, making up around 1% of Sweden’s 10-million population.2"

Ute Bohnacker (2022) Turkish heritage families in Sweden: language practices and family language policy, Journal of Multilingual and Multicultural Development, DOI: 10.1080/01434632.2022.2041646 https://www.tandfonline.com/doi/full/10.1080/01434632.2022.2041646