This is a very interesting question: many organisations (not just software projects) are struggling to adapt to doing research remotely. Luckily, lots of activities with users can be done this way, particularly if your users have access to a computing device and a decent internet connection (not all do!).
Pretty much all research activities I’ve done for FOSS projects (pre-Covid) were done remotely, mostly because that allowed me to reach users all over the world, and because it’s cheaper. Here come some notes based on my experience:
All the best practices for co-located usability studies apply to the remote kind.
Make sure to take some time to formulate your research questions, think about the profile of the participants, come up with appropriate tasks, go for the moderated variety to make the best of the time spent with your participants, and use the think aloud protocol.
To do usability studies remotely for desktop software, all you need is a video conferencing application with screensharing. I always recommend web-based ones (e.g. Jitsi) so that participants don’t need to install anything. Ask participants to share their screen with you so that you can observe what they do as they attempt the tasks.
With mobile is a bit more convoluted, but also possible with webcams or document cameras pointing to the participant’s mobile device, or screen mirroring software if your users know how to set it up. There are also commercial products to do this, but my experience with them has been poor.
Super easy to do remotely: either voice calls or video calls will do.
There are other approaches and ways that are suitable for remote settings:
Photography, audio and video. Ask your users to show you around using their mobile phone cameras if their physical environment is relevant to your research questions. For instance, their working space may be of interest to you: if they have more than one monitor, if they use alternative input devices, etc. They can also record video or audio of themselves as well as taking photographs and send them to you. For example, you may ask them to record themselves while they do something with your software, and comment as they go along. You may ask them to record a walkthrough of their computing device, telling you what kind of software they have installed and why.
Making. You may ask your users to draw or write something for you, or in some more alternative and less used approaches, to make something physical. For instance, you may ask them to create a diagram depicting the steps and sequence of events when they do a certain thing or complete a specific task with or without software. Or you may ask them to create a network diagram showing the people they work or collaborate with using which software and communication channels. They can then take a photograph of their artifact and send it to you, and explain it in detail during a video call.
Diary studies: remote by design, this method involves your users documenting their experiences in a certain format (e.g. a paper diary, mobile messages, etc) over a period of time.
There are many other ways, I am sure I am curious to see what others come up with.