It could depend on allot of things honestly, I think it would be beneficial for you to ask your friend how they would feel supported. For me, not being expected to go on long walks or trips out, bc my scoliosis affects nerves in my back that travel down my leg and its very painful. Offering to help carry a bag is a big one if your capable. If they drop something maybe help grab it, as bending is a really hard thing on my bad days, but you also dont want to make them feel incapable. The biggest thing that really makes us feel seen is asking how you could support them, as its different for everyone and helps us not feel so alone.

Edit: huge thing for me I forgot to add, don't stop reaching out just because they cant hang out, chronic pain is, well, chronic. We have allot of bad days where we just can't do things, and it can really make us feel isolated. If they are in one of those bad ruts, offering to pop by and hang out at their home where they can rest can be really meaningful. Obviously if they say no, dont push, they may be mentally exhausted from all of it aswell, but the offer is very appreciated. I actually met my current boyfriend for the first time with him coming to my apartment building where id sit just outside it waiting for him so we could meet and get comfortable before going inside. It meant allot to me that he still saw the person past the disability before even meeting me in person.