There used to be RV Parks that would offer cable modem connections to long term (monthly, yearly, etc) residents but I've not seen this as an option for close to 10 years now.
The majority of folks use cellular based data plans. Light users can even use a smart phone as a hot spot but it's not very convenient. Medium to heavy internet users will use either a stand alone hot spot with a data only plan for internet. OR a router with cellular modems built in.
A very popular option is Starlink satellite internet service. By all reports it's very good, however it is an expensive option.
It all depends on your needs. Light users may do fine with 50 gbs or less of data per month. But anyone using internet to stream TV or video or using the Net for work will need 300-500+ gigs of data per month.
There is a website devoted to nothing but mobile internet users. They have been around for more than a decade, and they are unbiased. They don't sell anything. You can read their reviews, instructions, and watch their videos for free. But to get more in depth info you have to pay to join the site for a year.
The link to that website is:
www.rvmobileinternet.com