I don't really like the term "fanboy" ( why just "boy"?) but if it's a synonym for fan, then definitely yes, maybe even more so now than when I was younger, but I'll try to explain why I think there's absolutely nothing wrong with it.
Companies are not our friends and they are not people. It seems obvious, but I think it's important to start with that. Being attached to the editorial line of a newspaper or broadcaster, to the historical legacy of a film studio or book publisher, to the know-how of a car manufacturer or fashion house, etc., is not the same thing as loving a brand as if you were a shareholder.
It's about loving cultural contributions, creative philosophies and, quite simply, of course, the memories and emotions that tie us personally to it. Being a fan of something is always linked to a context, to people, to things you've felt. In this respect, I'd say that I love what Nintendo means to me in much the same way as I love my favorite sports team, and for much the same reasons and based on the same springs. This doesn't mean being closed-minded, hostile or blind.
To tell the truth, liking Nintendo is probably what got me interested in video games in general, and therefore appreciative of other consoles, ever since I can remember. Being very happy with my SNES and Donkey Kong never stopped me from admiring Sonic on Genesis. It's funny, because one of the symbols of the famous "console war" was the opposition between the two Aladdin games released on SNES and Genesis, and my main memory is that I'd go to my neighbour house to play the Megadrive version and he'd come to mine to play the SNES version. They were just two great games.
Of course, the "console war" brought its share of idiocy, toxicity and problems, but I don't think it should be summed up exclusively in these negative aspects. The console wars also had a warm and communal aspect, often allowing for mutually assumed bad faith and therefore conviviality and fun. Assuring my friends that I was completely satisfied with my N64 and being sarcastic about loading times never stopped me from wanting to play ISS Pro Evolution, Crash Bandicoot or Metal Gear. In the same way, my friends who gently mocked the N64 limitations were happy to play Goldeneye, Mario Kart or Mario 64 with me. It was a form of good-natured rivalry, hence my parallel with supporting a sports team, but I was lucky that it was never mean-spirited.
Looking back, however, I realize that game consoles were also often a marker of social class. For a long time, I chose Nintendo consoles because they were cheaper, not just because I loved Nintendo games. It was pragmatic. I remember kids from more affluent families showing off at recess with their Game Gear, or even their Atari Lynx for some, and making fun of our Gameboys. It wasn't about their consoles or ours, it was just a way of saying they had more money, like with clothing and shoe brands. I must admit that the idea of having hours of fun on my old Gameboy with Tetris, Link's Awakening or Mario Land while their super-expensive, backlit consoles had poor battery life and few good games must have solidified my attachment to Nintendo.
So am I a fan? Yes, of course. I love Nintendo's culture, its history, its creators, its philosophy. Do I still sometimes act in bad faith? Yes, perhaps. For example, when I read including in this thread that Nintendo receives excessive praise and sometimes copies others, I can't help but have a "fan" reaction wondering why people remember applause when Nintendo is doing well but not the violent criticism when Nintendo is doing badly? And above all, I don't see when Nintendo has copied anyone. But I'm fully aware that I'm not being entirely objective here.
None of this is definitive, absolute or unconditional, of course. I'll conclude as I began: companies are neither our friends, nor people. The pleasure I take in what Nintendo has achieved with the Switch will never lead me to turn a blind eye, for example, to the scandalous and shameful situation of certain employees at NoA, to Nintendo's obstruction of the right to unionize, to the serious negligence that has led to the high frequency of joy cons drifts, or to the total lack of price cuts or select range of first party games, making them more difficult to access for the greatest number. In the same way, preferring Nintendo and hating what Microsoft stands for doesn't stop me from loving my Series S with the same pragmatism as when I loved buying a PS One or when I completely lost interest in the Wii/DS era. I like games, I like people, I like the spirit of Nintendo. That's what being a "fan" is all about. Nothing more, nothing too much.