There's no definite answer cause PvP and PvE are for different type of players. I think the real question is : who are your target players?

I don't think 90% of games have online multiplayer. Many games are just not designed for that. 

In terms of development, multiplayer is generally much more difficult to deal with, although there are also platforms that do some/all of the dirty work for you so that can help. The scope of the game obviously makes a big difference too. The advantage sometimes is that you have emergent gameplay coming from players actions, meaning you might have less work to do in terms of creating interesting gameplay (you just have to make the mechanics and then let players go to town). Then again, you might end up programming bots anyway to help with empty servers :P

Which is better, chocolate ice cream or vanilla ice cream?

No one can give you an objective and unique question, because PVP and PVE are not comparable values, they are different approaches, one focuses on making people compete against each other. The other, in making them cooperate.

As they are different approaches, some people enjoy one more than the other, in the same way that some people prefer vanilla while others prefer chocolate. The decision you make will attract one type of people or another type.

But neither decision is absolutely better than the other.

Personally, I think that PVP is much more complex to manage as a developer, because people who cheat can ruin the experience for the entire community and lead to the game failing.

On the other hand, in PVE, you can always implement private servers, so that a group of friends can play with each other and thus avoid people who cheat, something that does not work on a PVP-focused server.

What I do recommend is that you read a little, analyze how MMOs work, there is a lot of information floating around on the internet that could be useful to you.

By the way, I don't know what you are basing it on to say that 90% of games have online support, it seems like an exaggeration to me.

Of the 970,000 games indexed on Itch, only 18,000 have multiplayer, that is, 2%

On Steam, of about 100,000 titles, only 16,000 appear under multiplayer.

Many games have local coop and use tools like steam remote play or parsec. So really the number of games that natively support an online game are less.

You are not comparing pvp and pve. You compare multiplayer vs singleplayer. Both pvp and pve are multiplayer.

All three have their audience. If you are single developer, multiplayer is hard. Especially real time multiplayer. And there is the question, if it is mandatory multiplayer or optional. Is the core game a multiplayer experience, or is it just something that could be shared by several people playing together. Or is the game fun only there, because you can play against other players.

In games, pvp is very popular. It's just, that pvp is so often seen in real world. Be it chess or any sports.

I am hard pressed to find real world examples of pve. I believe those evolved from the fact that in computers and board games, you have to face the problem of a sore loser - and of grievous play. And pve is somewhat easier to implement in a computer game, than in a sports event. So they are there, because it is possible. You now only face the problem, if the pve game should be playable by one person or if multiple persons are mandatory.

It is a complex question and there is no straight answer. I depends too much on the type of game. And of your capabilities to actually implement any such game.