Recommendation for Forum Software

[GrAvEsSs]

Hello friends, I want to open a forum website for a project of mine. Honestly, I do not have the budget to invest in paid forum software because the market for paid forum software is quite saturated. What I need is an editable software that does not fall behind in terms of SEO. I have been considering SMF, but I have not made a final decision yet. Additionally, I would like to have a custom theme created for the free forum software that I will install. Can I get your recommendations?