One of the issues currently in Russia is the heavy propaganda and disinformation campaigns, as well as limits on access to truthful information.
If people inside Russia were better aware of exactly what is going on in the world, the support for the war in Ukraine could start falling rapidly.
If you own a website, have authored software, or regularly contribute to popular OSS projects, one of the options at your disposal is adding a message condemning the war, Russian actions, or overall sharing the global sentiment, or truthful information on what actions Russia has performed.
You could do this e.g. via geolocation if you don't want to bother all your users, but more global awareness is not a bad thing either.
If you have a website, you could also use geolocation to set up a blackout for Russian visitors, with a dedicated message condemning the war.
Know how to code? Submit a PR to an existing project and propose adding such messages into the software, explain the reasoning in your PR description, and maybe try to gather support for it via social media.
Some practical ideas can be found via the various "awesome" -lists:
Can't code? No problem, you can still e.g. submit issues requesting such messages to be added to projects, particularly any that are largely made in, or popular inside Russia.
Some ideas can be found from:
An example of such an issue: https://github.com/notepad-plus-plus/notepad-plus-plus/issues/11302
Lots of software auto-updates, which gives an easy way to distribute such messages.
Imagine Russians starting up Firefox to check something on Yandex, and Firefox includes messages on the titlebar. Imagine browser extensions sharing similar messages, SponsorBlock refusing to block ads on Youtube for Russians, or LibreOffice giving an alert message every time you try to open or save a document.
Imagine Russian developers trying to develop software during their normal daily job being greeted with notifications from
pip, and other every day tools condemning their government's actions.
Imagine Telegram and other messaging software sending notifications condemning the war to everyone within Russia every 12 hours.
Imagine if inside Russia software or games started refusing to launch, phones or cars refusing to function normally until the war is ended.
Yes, people can disable updates, make forks, etc. but it would become increasingly difficult to avoid hearing the truth.