Are there major contemporary poskim (halachic authorities) who advocate making nedarim (vows) for certain circumstance (besides donations)?
for example, someone who has a bad habit, to use a nedar (vow) to break the bad habit.
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Vows have always been discouraged. In fact, the gemara in Masechet Nedarim specifically mentions certain halachot of nedarim exist to discourage the light usage of nedarim.
Nonetheless, your example of using nedarim to break (at least certain) bad habits is indeed something that at least some major contemporary poskim support. GuardYourEyes.org is a resource for people who have addictions related to shmiras ha-eynaim on the internet. They openly advocate nedarim to break pornography addictions as one of the intermediate steps in their program. They have haskamot from many well-known and respected contemporary poskim including Rav Aharon Feldman, Rabbi Dr. Avraham Twersky, and others.
The formulas that the website mentions might not technically be considered nedarim under the most literal definition of the term; however, they are commonly referred to as nedarim, and could potentially be formulated in a way that is a technical neder.