I enjyoyed a sauna with friends today. I enjoyed a sauna with friends today.

Spelling.

I enjyoyed a sauna with my friends today. I enjoyed a sauna with my friends today.

I don't believe "I enjoyed a sauna with friends today." is necessarily wrong, I just think that it feels incomplete without a qualifier for "friends". Alternate suggestion: "I enjoyed a sauna with some friends today."

I enjyoedoyed going to a sauna with friends today. I enjoyed going to a sauna with friends today.

One of themy friends haves a sauna tent, and we tried it near a river. One of my friends has a sauna tent, and we tried it near a river.

"the friends" feels a bit impersonal. It's how you would describe someone else's friends, but not your own. So it's best to refer to your own friends as "my friends".

One of the friends haves a sauna tent, and we tried it near a river. One of the friends has a sauna tent and we tried it near a river.

A few alternate suggestions: "One of the friends has a sauna tent which we tried near a river." "One friend had a sauna tent and we tried it near a river."

One of themy friends haves a sauna tent, and we tried it near a river. One of my friends has a sauna tent, and we tried it near a river.

Outsidedoors sauna iss are becoming popular in Japan, but someon people still think it i's difficult. Outdoors saunas are becoming popular in Japan, but some people still think it's difficult.

I'm not quite sure what you mean by it being "difficult". Usually "difficult" is used to indicate that a situation is challenging, but this sentence isn't presenting such a situation.

Outside sauna iss are becoming popular in Japan, but someone still think it i's difficult. Outside saunas are becoming popular in Japan, but some still think it's difficult.

When referring to a general concept instead of a particular thing, e.g. saunas in general instead of 1 specific sauna, you usually use the plural version of the word. Also, almost everyone uses the contraction of "it" and "is" (which is it's) in both written and spoken English (at least, in American English).

Outside sauna iss are becoming popular in Japan, but someon people still think it is difficult. Outside saunas are becoming popular in Japan, but some people still think it is difficult.

Today, the weather iwas pretty good and warm. Today, the weather was pretty good.

To a lot of people "good weather" already implies that it is warm and not raining.

We were very relaxinged. We were very relaxed.

Here you should use an adjective, thus "relaxed" is the best choice. You could also say "it was very relaxing".

We were very relaxinged. We were very relaxed.

We were very relaxinged. We were very relaxed.

"relaxed" -> the feeling you feel. "I was very relaxed" "relaxing" -> the effect of causing someone to feel relaxed. "The sauna was very relaxing"