Assuming you meet other eligibility requirements, you can shop for coverage on the marketplace during open enrollment or a special enrollment period if eligible, but if you have access to job-based coverage, you might not qualify for premium tax credits.
When people are eligible for employer-sponsored coverage, they can only qualify for marketplace premium tax credits if the employer-sponsored coverage is unaffordable. The way this is calculated, coverage is unaffordable only if your cost for coverage for a single person under the employer plan is more than 9.61 percent of your household income in 2022 (for 2021, it is 9.83 percent of household income). (IRS Rev. Proc. 2021-36)