Not to excuse these dark patterns from shitty products that can't get revenue without tricking people, but privacy.com lets you set up single-use credit cards with e.g. a $1 lifetime limit. This is my go-to for places like this if I really, really want to try it.
You might enjoy the binaural beats and ambient radio on https://ambiph.one as a free alternative (disclosure: it's my site). Not as science-y as brain.fm but it helps me a lot with focus
I have ADHD (professionally diagnosed as an adult) and basically cannot focus without music. I complained at work about endpoint management software that was interfering with my music player and was told I didn't need to listen to music while working.
I WFH so I just found another way to play music, but it was tempting to point out to my boss (who I otherwise quite like) that he had just told me that I shouldn't be using a reasonable accommodation for my disability that costs the company nothing, lol.
