Smith Park in Allston/North Brighton. During the summer time, I think on Tuesday night, they have roller skate dance party there. You should check it out. Pump track there too.

https://www.wgbh.org/news/local-news/2021/11/12/skating-is-like-therapy-for-bostons-skate-hags

You can take #70 bus there from Waltham. I see people roller skating weekends.