Any employer, including self-employed individuals, can establish a SEP plan. Contributing to a SEP IRA won’t prevent you from also contributing to either a Roth IRA or a Traditional IRA. However, access to a workplace retirement plan might impact if you can deduct Traditional IRA contributions.
A Simplified Employee Pension (SEP) Plan IRA account or a SEP IRA has different contribution limits than a Traditional or Roth IRA.
Information on contributions to a SEP IRA can be found at the following IRS link: SEP Contribution Limits (including grandfathered SARSEPs)