In some cases, yes. In fact, one of the Irish mobile operators currently has an all-you-can-eat prepay sim top-up promotion that gives you unlimited 4g data for €20 every 28 days.
They have a fair usage policy but don't enforce it (no idea why) and chatting with their pricing personnel it makes no economic sense (they lose money on it). It would appear it's a sacrifice they are currently willing to make to ensure market share increases.
Yep, I have this and often just teather up piles of people. Never have to think about usage. Now that I mention teathering, I don't think there are any Irish service providers who attempt to monitor or regulate teathering, which is nice.
Lithuania here, unlimited from cellphone operator for around 29 eur/mo, I don't see anything forbidding tethering, I know you can ask for a data-only clone of your SIM to put in your car or laptop. You can get a better deal from the operator that specializes in 4g internet only if you are within coverage.
Uk here, yes, I have a truly unlimited plan including tethering. We used it as our main house connection for three months when we moved into our house, while the 250/20 main line was being fitted very slowly. I pay around £20 per month.
One example: https://tuki.dna.fi/org/dna-en/d/dna-rajaton-prepaid-support...