The following graphic, provided by the Thai Tourism Authority in conjunction with the National Park Service of Thailand, shows the current status of all National Parks in the country during a cluster of Covid-19 infections.
Unlike the first round of infections last year, most parks remain open during the current situation. Here is a graph that shows their status. Keep in mind, Thailand still has many travel restrictions depending on the province, and people in highly controlled provinces (like Chonburi) may be required to do a fourteen-day quarantine and will need permission to leave their province for essential reasons only. Going to visit a national park would not be an essential reason.