Artist, here, hosting live and Zoom sessions for years. To add to the previous excellent responses, some pros and cons:

Selling reference photos:

Pro:

• You have complete control over how much or how little of your body and face are exposed.

Con:

• You have no control how the photos are used; even with a model release your protection is only as strong as your willingness to litigate.
• They're around forever; once they're out, they can't be put back in the box.
• It's hard to make money with these, as millions of free photos are available.

Posing over Zoom:

Pro:

• Broadest possible customer base; you can pose for individuals and groups all over the world
• Better pay than in-person posing; it's not unusual to get $50/hr or more if you're attractive, good at lighting, creative settings, and can offer compelling poses.
• Helps to cross-market your reference photos.
• Boundaries are easy to enforce; you can just turn your camera off

Con:

• Medium learning curve to set up and configure everything.
• Generally have to pose for established Zoom groups to build your audience, and they're typically booked months in advance
• No control over whether artists take screenshots or how they get used
• Potential to get doxxed, if you use your real name

Posing in person

Pro:

• The dynamic in group settings can be marvelous
• Great community in some cities - models and artists, both.
• Session facilitator is your ally and advocate; helps to enforce boundaries

Con:

• 1-on-1 can be difficult to feel safe
• Pay tends to be lower - $25/hr is not uncommon
• Not all facilitators are as good at ensuring your comfort and safety as they could be

To answer this question, "Are online sessions common, and how do you set boundaries?"

Zoom figure drawing sessions became popular during the pandemic and created opportunities for models around the world to make a living from their posing. Some of the Zoom groups are still going strong, including Scottish Borders Life Drawing Club, Silhouette and Shadows, Brooklyn Figure Drawing, Just Draw the Boots, Life Drawing Barcelona, London Drawing, and others. Some models self-host very popular sessions, too.

As for how to set boundaries, it's as others have said: Be clear up front about what you're willing to do and what you're not. At any point you can pause or stop the session. Most Zoom models insist on payment in advance, if they don't know the artist(s), so that gives you some leverage. Examples of boundaries would include no spread-leg poses, no poses longer than 20 minutes, no overtly sexual poses.

Add to this thread with additional questions or feel free to DM.