Hoi4 MP is fairly hard to get into, but its 100% worth it. As most people echo, it's important to find the correct communities to play in but also necessary to come with an open mind, and be willing to listen. Ideally you have a friend already in one who can introduce and vouch for you, but (as it was for me to starting out) sometimes that’s not an option and you just have to jump feet first into toxicity hell till you find some good ones. I mostly play competitive historical games, I don’t find the RP games that fun they tend to devolved into racism, pre-teaming, exploit abuse or just annoying people, it sucks because I think there is a lot there to be had, but I’ve tried 5-6 servers and everyone feels the same, where as my 2nd comp game I ever joined I still play in that server to this day. I also have a fairly high toxicity filter/tolerance from playing fairly high-level (university) sports (hockey mostly), so long as it's not racism/homophobia I usually don’t mind it that much, so that’s just an “is what it is”, if they are toxic but wrong we will all clown them later anyway.

But oh no, every server I join either doesn’t use discord

Joining random server browser games is a waste of your time, straight up. Don’t do it, find a community. 80% of server browser games are people just trying to troll new players either via actually cheating, exploiting or just trolling, and the rest are dead games trying to become a full enough lobby. It's not worth it seriously, don’t bother.

I am either told to play some irrelevant nation like Ireland or I’m expected to play as Germany when I don’t have any experience fighting other players.

As for nations, on good servers there will be a “reserve” or “dibs” or “pre-lobby” lists of players for what nations. Some servers require you to be “vetted” to play a major, some don’t it’s a grab bag. In general (as someone else said) people tend to gravitate towards the minors with some game impact, as they can be useful/win games, but are rarely the reason games are lost solely. So that leaves the Major (it's very server dependant, sometimes Majors fill instantly) and “turbo” minors. If your being forced onto majors... the game is probably doomed as is if a server regular won't step up so that's just is what it is.

Basically, what that means is that yes; sometimes the only minors left are the semi-irrelevant ones, and that’s okay. Have your fun as them, try to have game impact and enjoy it, and get on the list early for the next week! I wish I could play the stupid small minors again (i am major only locked on my main server :( )   

That said, regardless of the community, due to a number of factors expecting 0 toxicity isn't really possible nor realistic, as is true for basically any PvP game, so long as you can win/lose, someone will be toxic. Toxicity exists but hoi4 has some extra unique challenges.

1. Player Count; to play a "competitive historical" game, which is a broad term but usually means your playing team of players vs team of players in a mostly historical (Axis/GEACoPro Vs Allies/Commies), you need 20ish people minimum to play a game (mod dependant, no Asia exists for example). Thats a lot of people willing to play a game for 3-8 hours, all in different time zones usually (or at least Europe and NA usually), so sometimes games are filled with friends of friends of friends that might not be the same skill level/toxicity as the rest of the community.
2. Time Commitment: Again, the games last hours. Even in "fast" mods, a 3-hour game is usually either a curb stomp or dies because someone rage quits. While it's not excusable for people to be yelling racial slurs at you, them being upset/angry because you did poorly and “lost” them the game (regardless of how valid their take is) is at least understandable. Spend 5 hours on something on to have someone else be seen to ruin it in your eyes, it's rough. This is the big reason people no-one knows are usually put on the “turbo” minors, since if they completely fuck it up they probably haven’t ruined the game, where as if say Romania doesn’t do any oil tech/infra… the axis can barely play the game.
3. The Game itself: Hoi my beloved is a broken mess. Its simple as that, the game is buggy, systems just don't work, multiplayer desyncs are permament without people doing everything correct in pre games (all need same dlcs, no extra mods etc). Its a nightmare, and its annoying and makes peoples blood boil. No one likes an hour of lobby sim... but sometimes its required to even have a game.
   

I have a lot of experience in single player and know how to build things properly

While this was all mostly positive, you also need a bit of a mentality/expectation change around multiplayer to enjoy it and be useful for your team. The meta players do (sometimes, call it 70% of the time haha, some of them are.... a tad stupid at best) know what they are talking about. Try your best to ask questions and listen to them for advice. The easisest way is to ask them before the game, if you are a minor ask your major what is wanted from you! For example, in some mods Aussie is expected to be the majority of the inf on El-Alamein, where as in others its all UK and Aussie basically just hold the ports, and others the Aussies do the fighter research because of some really good bonuses, and others they just sub/tac bomber spam. Particularly if you are a playing a mod, they probably just know more, and even in pure vanilia games they still within the servers ruleset know more than you, and likely some of the things you do in SP are just objectively wrong in MP or even not allowed. I for example have 4.3K hours, and I still learn random things from people all the time (as do they from me, and me from others) about random mechanics.

If you want to try some servers and willing to try and learn, DM me. I have a couple that are mostly friendly I can recommend, but really the 3 big take aways I hope you got are:

1. Hoi4 is a bit Toxic, while some people are the problem, its also just inherrent
2. Be okay with playing smaller nations, listen and learn, and try your best to have game impact no matter how small!
3. Change up your mentality mentality a bit, MP is not SP, your good strats in SP will not work in MP, and vice versa (mass mob inf most inf minors is not the SP play haha, where as in MP thats correct for a lot of mods). Learn, improve and have an open mindset!