Promote social interaction. Often, organizations take such a pessimistic view of remote work productivity that they set unreasonable expectations, discouraging people from having social conversations via online collaboration platforms. But while discipline and focus are important, a lot of organizational culture is transmitted during informal social interactions, which can get lost online.
At minimum you should designate a channel on your chat platform for team members to have social conversations and post things like movie recommendations or photos of children and pets.
Beyond that, examine any activities or rituals that depend on physical proximity, identify their underlying intangible value, then find other ways to capture that value virtually.
Does everyone look forward to the annual holiday party? Help people express their holiday spirit by organizing a (voluntary) gift exchange and offering to have the company pay for shipping. Do you have a team that plays against other organizations in a local sports league? Maybe do a monthly trivia contest so people can flex their competitive instincts.
You can also create communities of practice/interest. For instance, create a social network for women managers in your company or encourage people to set up things like after-hours online book clubs or even cooking classes, which can be promoted via company platforms.