At the peak of the pandemic, some reservations tried to restrict access, but had some conflicts with the covid-denying state governors. I mainly remember news items about this from South Dakota.
The Blackfoot Nation web site notes
Despite loosened COVID-19 restrictions by the state of Montana, the Blackfeet Nation is still exercising caution
https://www.hcn.org/articles/indigenous-affairs-covid19-tribes-defend-themselves-against-a-pandemic-and-south-dakotas-state-governmenthttps://www.travelsouthdakota.com/sites/default/files/2020-07/southdakotadepartmentoftourism_tribalcheckpoints_07292020.pdfThe check points probably don't exist now, but tribes might still expect masks and social distancing beyond what the state expects.