Fertility rates will stay below 2.1 for at least 200 years
Fertility rates have been falling for centuries. It isn't something that can be quickly fixed and it requires massive changes to reverse. No political party will ever take the large risk, especially since there has been no proof of a solution yet i.e. a developed country returning to 2.1 fertility rate. Another major reason is immigration. There's little reason for governments to take the large risk when immigration already addresses the problem. Developed countries aren't going to act until the immigration tap runs dry, which is unlikely until 150+ years later.
Politics aside, I doubt people will ever reach consensus on a solution. Everyone has their own theory. The lack of consensus will just cause slow progress and insignificant changes. The only problems that are commonly cited are cost of living and housing. Realistically, governments will never solve these issues and there are large conflicts of interest as some people want house prices to rise. Regardless, solving these issues is unlikely to return fertility rates to 2.1 as fertility rates were already <2.1 before 2000 when cost of living and housing were cheap.
Fertility rates reversing will never occur due to unanimous agreement. It will occur when population decline starts having major impacts on the country, e.g. economy crashing, massively diminished populations, and high old-age dependency ratio, which will force people to change. This isn't going to occur until 100-150 years later (depending on levels of immigration). Once change occurs, it will still take 50+ years for fertility rates to rise significantly since it will take a long time for people to adapt to the changes. People aren't going to start having many babies immediately in most scenarios. Also 100-150 years later, I expect the fertility rate to be <1 by that point and people to have become accustomed to low fertility rates, so returning back to 2.1 will take much longer than now. Keep in mind that the UN projected fertility rates to be 1.59 in 2100 in the medium fertility scenario, and based on new data, that's obviously an overestimation. The low fertility scenario projected fertility rates to be 1.1 in 2100 and not change much this century.