The original series is very 1960s and I wouldn’t recommend for a jumping in point. I’d go with next Gen for that, it’s the quintessential trek more so than the original having had 3 spinoffs in the 90s and defining most of the canon. Here’s the issue though, the first 2 seasons of tng really suck. Like maybe the worst 2 seasons of the whole franchise. I’d check out some best of lists for those seasons and maybe sprinkle a couple random ones in, they did 26 hour long episodes per season and there are some amazing clunkers there, bad episodes are part of trek and you’ve gotta learn to enjoy them, but those first 2 seasons are rough.