The newer omicron sub-lineage BA.5 currently accounts for 65% of all new COVID-19 infections. This variant is rapidly gaining ground because it is far more transmissible than any of the COVID-19 variant predecessors. This increase in viral transmissibility has in turn led to a surge in US COVID-19 cases, with a 7-day reported average of over 100,000 cases per day (and keep in mind this doesn't include home tests!). Hospitalizations have also increased with these new sub-lineages, especially in the 70+ age group. Considering that BA.5 is having real health consequences for communities, it is advisable to layer as many mitigations as possible this summer when gathering with others.
All things being equal (size of gathering, activity, group of people, etc.), it is safer to have an event take place outdoors vs indoors, but the risk of transmission is still not zero. The risk of infection also increases the more crowded the event, even outdoors. For example, an outdoor lunch with 5 people on a patio would likely entail less risk than attending a crowded outdoor concert where people are packed in body-to-body. The fact that these two events are both outdoors does not make them equally safe activities.
Ventilation is the mitigation layer that we use by moving a gathering outside, and it is only one layer of mitigation out of many that can prevent COVID-19 transmission (along with masking, vaccines, distancing, testing before gathering, hand washing etc.). No one layer is 100% effective, but altogether they can work as a system. The higher the prevalence of COVID-19 in the community (and the more contagious the variant), the more layers of mitigation we need at a given time. Considering these more transmissible sub lineages BA.4 and BA.5, It is advisable to use multiple layers of mitigation even if you will be outdoors. For example, be up to date with your vaccinations and boosters, monitor yourself for symptoms before, take a rapid antigen test before gathering with others, or wear masks if it is a crowded outdoor event.
Unfortunately, the more transmissible a virus is inside, the more transmissible it will also be outside. But, if you limit the size of gatherings and take sensible precautions, outdoor events can be a safer way to socialize this summer.