Baseline research on support for the fullscale invasion:

https://www.levada.ru/en/2024/05/17/conflict-with-ukraine-assesments-for-march-2024/

The level of support for the Russian armed forces has not changed significantly since the beginning of the conflict – the majority of respondents (76%) support the actions of Russian troops in Ukraine, including 48% “definitely support” and another 28% “rather support” the action of Russian army. 16% are against.

Research with preference falsification adjustments with respect to support for the full scale invasion:

https://journals.sagepub.com/doi/10.1177/20531680221108328

when asked directly, 71% of respondents support [full scale invasion of Ukraine], while this share drops to 61% when using the list experiment

Support for annexation of Crimea:

https://www.levada.ru/en/2021/05/19/crimea-3/

The vast majority of Russians (86%) consistently support the accession of Crimea to Russia – this indicator has fluctuated slightly since 2014. 9% do not support the accession.

Research with preference falsification adjustments with respect to support for annexation of Crimea:

https://www.jiia.or.jp/en/column/2022/09/russia-fy2022-01.html

Using the list-experiment technique, Timothy Frye and others showed that Putin’s approval rating after the annexation of Crimea was actually high, at around 80%. In their study, they made a list of famous Russian politicians and had respondents answer how many of these politicians they supported. They then estimated Putin’s approval rating by adding the name “Putin” to the list for only one group[*]3 and thus concluded that the high approval ratings after the annexation of Crimea were not very different from the findings of opinion pollsters.

A high level overview of russian support for the invasion of Ukraine (a summary, but with links to relevant research, albeit some sources will be in russian):

https://www.atlanticcouncil.org/content-series/russia-tomorrow/reluctant-consensus-war-and-russias-public-opinion/

Younger people still support the war in high numbers, though their support is lower than that of the older generation: 75–80 percent of people fifty-five and older support the Russian army’s actions in Ukraine, while 61 percent of young respondents in Levada polls share this sentiment.