What resistance? It seems to me that there is not one big organised resistance that is taking members.
Find a local event and network but be careful about it. The US had that "no kings" thing early in the summer (or before?). That was just a bunch of people against tyranny. No real organisation to it. So you'd go to something like that and just talk to people.
It helps if you have an anonymous way to chat. Something like Signal or Matrix or one of the others. Even Telegram would be better than using something public or corporate-backed, like SMS for the former or WhatsApp for the latter. But be careful with Telegram, read up on it, it's not a solid recommendation but it's better than nothing. Fortunately there are alternatives. Even if the other person isn't tech savvy — you probably are by being on Lemmy. So, show them the way.
Occasionally contact them through anonymous chat, just see how they're doing, and discuss future plans.
Also, aside from demonstrations, places where like minded people meet. For the authoritarians and conservatives, that's church, the local BBQ spot, and other, more obvious groups. I feel like they feel they can operate more openly since the US president is one of them. Used to be, these guys wore masks and were hidden, joining them wasn't about finding them, they'd find you, that kind of thing. Nowadays it's all out in the open. But I think liberals and progressives have meeting places, too. In response to church, for example, you should know that The Satanic Temple is not about devil worship, they're about resisting Christian imperialism. They're the ones fighting churches trying to get the Ten Commandments posted in every classroom. I'm religiously neutral, so they do not interest me, but they're certainly an option. For the anti-theist/"hard atheist," they're a good option.
Being that I'm the husband who has drunkenly tried the dancing games, I would say my wife is finding the Rockband exhibit. So we don't really go to arcades. We do sometimes stumble into the game room at conventions. And someone always has a modded Xbox 360 and Rockband 3 set up with all the anime songs on it. And you can generally just step up and play. When a lot of people want to play, there's a queue and a system for doing it, but most times we go, you kinda just glance toward the person singing or drumming or whatever you want to do, and they pass off to you when they're done with that song, or ask if it's cool if they do one more, maybe that's their pick they waited for or something. Anyway, I suck at arcade games, so I'm grabbing the Rockband mic. No one wants to sing in public, especially if it's in Japanese and we don't know it. The lyrics are described in romaji (e.g. "arigatou gozaimasu" for ありがとうございました which is to say "thank you very much" and is pronounced something like "ah-dee-gah-tow go-z-eye-moss"). As someone who can pronounce maybe 10-20% of romaji correctly and can kinda wing the rest... it's fun. Plus we turn the mics down and the vocal track up, so if you mess up, you don't ruin the song for the onlookers (you can do the opposite and only hear the vocalist, for example).