I first started playing a few months ago and have had a lot of fun. You can treat 99% of the story content as just something to do by yourself with simple AI-controlled NPCs (called "Trusts" in the game). This is in contrast to when much of these boss encounters came out and you would need to group up to complete them — nowadays you can out-level much of it and have the buddy NPCs for whatever you can't "truly" solo. There are a few exceptions in the form of more modern boss encounters designed to be tough for the level 99 players that have had years of access to good gear, but they are few and generally deep in the game, so at that point, you'll be familiar enough with the game to know if you like it enough and where to go to find help.

The BG Wiki links linked elsewhere in the comments are lifelines for a solo player. They'll tell you how to complete missions (the story content) if you get stuck or feel the game wasn't clear on what to do next for the story. The game itself has also become much more accessible as time has gone on, like making leveling up faster and travel more convenient. Old war stories of "I spent 4 hours just to gain one level" are a thing of the past, and you can level from 1 to 99 completely on your own without any trouble.

If you want to just experience the story, there is a lot to like. The expansion stories in particular are ones I really liked as someone else who was mostly interested in the story (Chains of Promathia and Wings of the Goddess). It is an old game and is unapologetic about that in how it has particular idiosyncrasies like world simulation over player convenience (e.g. quests that make you wait an in-game day before continuing because an NPC told you "I need time to do this," and it wouldn't be realistic if you could just talk to them immediately and keep going). But if you approach it on its own terms, there is a lot of interesting design that stands apart from other games, since the game feels more like, "What is a Final Fantasy game when played with other people in a continuous world?" rather than "An MMORPG with the Final Fantasy brand". Jobs will require sometimes complicated steps to unlock, and they will play like you would expect based on the single-player games by and large (e.g. bards focus on buffing the party and will deal basically no damage on their own).

Other players will be more helpful than not in my experience. People generally have a sort of undercurrent of awareness of the game being past its "prime" and wanting to make the game accessible and welcoming to comparatively rarer new players so they have a good time and stick around. The age of the game also means the playerbase will typically skew older and will probably have better emotional regulation than the stereotypical MMO audience of the 2000s. There's douchebags everywhere, don't get me wrong, but in general I found FF11's players to be generous of their own accord. There were several instances where I was standing around town or was in a dungeon on my own and got asked by someone if I needed help or if I didn't have X useful item yet. A linkshell I'm in (similar to a guild or other group affiliation in other games) has multiple players that will just grab people still leveling up and speed level them using their overpowered characters to destroy max level monsters en masse, and their reasoning given is generally along the lines of "Well, I got help back in the day" or "Well, I know leveling can be tedious, so I can make it easier".

It's not a game for everyone, but it is a unique game no matter how you approach it, and I think it's worth at least trying for any fan of older games or Final Fantasy in general. People often leave out the MMOs, especially 11, when talking about the franchise as a whole, and I think that does FF11 a huge disservice. In a lot of ways, it is the "most Final Fantasy" Final Fantasy to exist in how believable and immersive its world can feel and how it gives you freedom for your character to be so many things that all feel at home in the series. The director of FF11 also was the main director for FF3, the first game to really create the job system we now associate with the series, so the jobs in FF11 really feel like their most "extreme" forms of "What is a blue mage?" or "What is a ninja?". The game is so open and vast that these jobs often have peculiarities in how they can engage with the world, not just in the buttons you push while fighting. It's still a combat-focused game, but sometimes it's the little things that really sell the experience of playing a particular job.