2021: buying the Edge 830 or waiting for 830Plus/840?

The Edge 830 is fine. I don't know what measuring stick is being used to call firmware "buggy", but I disagree with that characterization. These same whiners probably say "don't buy an iPhone, the firmware is buggy".

Seriously, you're claiming 830 firmware is buggy and promote the Karoo Hammerhead? That unit is officially more or less still in beta and was alpha for a long time and for me is the definition of buggy and lack of features (admittedly, they are getting better). You cannot be serious or have some Garmin issues..s

The only difference between the 830 and 840, will probably be a buggy bike computer that you can charge up quicker.

I never understand all those complains about the 830, it is from far the best GPS on the market, I do every update, inclusive all beta's, (and raiderma I never pay a penny for). OK, sometime it happens that something goes wrong, but each time it is resolved by an other update
I think the problem from some is that they could not understand that the 830 is priorly a GPS, it is not a fridge or microwave, I never use the machine for anything else (perhaps, if I thing about it , the notification from the iPhone).
If one day they made a new 830 plus or 840, I hope I can put a memory card, it is the only thing that I want to improve , 16 GO is not enough for me

I agree, I love my 830.  Only issue I have had is with crash detection and how easy it is to indicate you don't need and SOS.  That was a bit tricky a few years ago but Garmin has refined that.  It wasn't buggy, just the 1st revision was not a great interface.

I ride 3 or 4 x per week road and MTB, I have multiple sensors, dual sided power meters, The Garmin is controling my Bontrager lights, Dura Ace brakeset lever remote switches are paired to control the head unit on my road bike and a Garmin remote to do the same on the MTB.  I use both trail forks and Garmin navigationm. I also use love track, group track and incident detection.

Not a single issue, what bugs have you encountered?

I also recommend the 830 - it seems that garmin have turned a bit of a corner regarding their firmware. The x30 series have far far fewer issues than the x20s.

A previous poster said "look at this forum" but honestly this place is dead compared to what it was like with the massive problems on previous products. I think it will be a while before Garmin loose their reputation for buggy firmware but their latest devices are a massive step forward - I dare say that it's the wahoo devices that I see the most grumbling about recently - so a totally reversal of what it was like 2-3 years ago.

I had a 1030 and sold it because it felt a bit slow and I thought I would try something else. I bought a Hammerhead Karoo 2 and it whilst it had a lot of promise, it's far more of a beta product than anything Garmin make. Useless battery life, buggy sensor code, fragile mounts, the list of problems was endless. I bought a heavily discounted 830, and I am really happy with it. 

Wahoo doesn't have their own forum for complainers to gather, either, so you would have to do a lot more searching to find user complaints.