I try to learn something but I do not understand following:

It is said that bitcoin private keys from any generator are provided in BASE58 format

on this page I found many examples for private keys:  https://bitkeys.work/

It should be that bitcoin uses secp256k1 ECC  ?  So private key is 32 bytes?

here are some decoded private keys into hex from abovementioned page:

L52sDjGxf8Y5NHy5BjTpQHQUjHDjrqErHyTomskefFXrKPdjf7Di                                                        base58
80e91ed90e9a784499a4e37580de2f5d6b622ba96ff1f735f1992ce787575a44d9010c3e5e49               hex

L2HBA8KcR57PYoGCbZmKUNvmhu7SsrupYj172fQAGkgY75sGUjHQ
8096f833ea1ee11688ad8718e37b3ea81e76911eabed36bbeadb42b6e08b669ee4013cd4ac07

KwXvqELPvZUFgFZ5RhWWLQJQrPvEbk6WKktBk5smCqBeLc17uEvQ
80095f3f838b21709382525317062ada9231188e60304eaaf3d287ed7e7a8c825a01252f78ad

WTF, why private key is not 32 bytes long after decoding base58?  But it has got 6 bytes more?
Also 80 at the beginning seems to be very suspicious....

Any clarification will put me back to a sound sleep during the night...

I am a total newbie with GPU calculations so please be patient with my questions.

I have Nvidia Quadro P4000. I need to find private key from public key 256bit ecc.
The Kangaroo seems to be unable to cope with this task. I know it can be supported by GPU but here I do not understand how much of GPU is really used by Kangaroo. What I have seen here it uses maximum a few of tens of GPU threads. But gpu has got thousands of them? Also to be sure Kangaroo is bugless is a bit fantasy. Also difficult to debug. Does Nvidia card need monitor to be connected or to have that special dongle virtual monitor from Aliexpress? How is computer creating screen if nvidia is used for calculations?

So I have this idea, please try to understand and estimate if it is feasible? I want to use whole gpu, 1024 threads or more. Each thread would search in a brutal way the private key in very simple manner: instead of multiplying generator point every time with new possible private key I would start every thread on its own ?? -bit space. It would start from initial "private" key and continue with adding generator point, this would be much faster. After adding generator point (+1 gp) gpu will also check X coordinate if it fits already to public key. Easy to debug. So I would have 1024 gpus performing simple task adding generator point and compare just one coordinate, say X. If it would work but one gpu P4000 is not enough maybe GPU cloud rent for 1000euro for 1 month might be enough? At this moment I have no idea how much time would gpu need to perform one iteration step so I welcome any estimations from you.

What would happen if everybody wants to exchange for a real money?
I consider it not fair to mine cryptocurrencies?
If it is so good why there is a need for exchange rate to the real money?
Why recently I needed to block about 30 phone numbers constantly calling me to invest money in cryptocurrency? Is it going to finish soon because of having probblems not to be fed this pyramide game with real money?

I hope I will pass on this forum with my question though it is not about secp256k1

I want to adapt BSGS algo for eliptic curve secp256r1

Order n is smaller value than for k1 curve. Also it is claimed n is prime for r1. So I hope the m value for Montgomery arithmetic should fit directly also for r1?

I know I need to change some constants like 10003D1 and so on...

Anybody has experience implementing eliptic curve r1?