Suggestions for Forum Software

[GrAvEsSs]

Hello friends, I want to open a forum site for a project of mine. To be honest, I don't have the budget to opt for paid forum software since the market for paid forum software is quite saturated. What I need is an editable software that is not lagging behind in terms of SEO. I am considering SMF, but I have not made a decision yet. Additionally, I would like to customize the theme for the free forum software that I will install. Can I get your suggestions?