If you just want autocomplete (it can’t do debugging features like breakpoints) there is a script editor on the asset store that runs within Unity. Last I had heard it worked on Linux but I don’t think the developer officially supports it.
Just in case you’re not aware Rider’s subscription has a perpetual fallback aspect to it. Any versions that were available to you for an entire 12 consecutive month period will still be available to you after you’ve stopped your subscription.
For example I just checked my account and I’ve been subscribed since August 19th 2021. As I’m on an annual plan my fallback version is 2022.2 which came out August 1st 2022. Once my plan renews next month my next fallback version will become 2022.3 which came out December 6 2022. If I were monthly I’d have to wait till December.