The transaction which paid 50 BTC to that address did not pay that address at all. Rather, it paid the public key associated with that address, as Charles-Tim has pointed out. Most wallets and block explorers will therefore not show the transaction or not show it correctly, although some do.
The private key 5KGLRScL6BqRkWnB8kTtoJmj21GT2W4KHpHJ2AA6vewuqM3tFVM gives the following uncompressed public key:
044e01f16fe203dbfd8110fd636f42e69bd2fa9e0fef913f00554e4412cb1cae070296f95c6b64f3fdcb7ee9dc838f20b992077e839703b3c2c5427e90e5afd0d1
That uncompressed public key gives the address you have shared.
Let's look up the transaction which looks like it pays that address 50 BTC:
https://mempool.space/tx/4ff149267a5b1e55e3d90a5a5b451dd6d3c2c82b26b96a599dda0ed5585f1f3dIf you click on "Details", you'll see that the locking script is simply OP_PUSHBYTES_65 PublicKey OP_CHECKSIG, and the transaction type is P2PK (pay to public key).
And so, because this is a P2PK transaction paying a public key, and not a P2PKH transaction paying an address, Electrum will not display it. It will however show up on some block explorers, for example here:
https://blockchair.com/bitcoin/address/1NChfewU45oy7Dgn51HwkBFSixaTnyakfj