There are many different variations on this question: What if the in-person conference was canceled but it moved online? What if the conference was held, but I was unable to attend due to COVID-19 travel restrictions?
If the conference that accepted your presentation was canceled, you may list the presentation on your CV under a header such as “Accepted Papers” or “Invited Speeches” and note that the conference did not take place. The following provides an example:
Chen, Joanne. “Strategies for Teaching Grammar to First-Year College Students.” Conference on College Composition and Communication, Milwaukee, WI, 25–28 Mar. 2020. Conference canceled.
APA recommends this same sort of thing, but also provides some additional guidance:
If the conference moved to online…cite it normally – no need to specify that the presentation moved to an online format. Online-only conferences use the same template as in-person conferences. (And you still include the conference location.)
Kullgren, K., Carter, B., Caplin, D., Ramirez, L., Williams, S., Marsac, M., Judd-Glossy, L., & Brown, M. (2020, March 19–¬21). Pediatric psychology consultation: State of the art and future directions [Conference workshop]. Society of Pediatric Psychology Annual Conference, Dallas, TX, United States. https://societyofpediatricpsychology.org/node/726
For other style manuals, the format may vary slightly but they will have very similar concepts that can be applied using the above examples.