Could somebody write a private GPU miner? For nonce search, yes.
But nonce search is only the second phase of Parano1d mining. First, the node must build a new HistoryStep proof for every parent. The current prover is CPU-only and optimized for binary-field arithmetic through AVX2/AVX-512 VPCLMUL on x86 and PMULL on ARM. There is no CUDA or OpenCL prover. A GPU nonce kernel cannot build this proof. It must wait for the CPU, and if another block arrives first, the prepared work becomes obsolete.
A GPU may still gain something during nonce search because it can run many independent attempts. How much is unknown. Poseidon2b over GF(2^128) is not SHA-256. Modern CPUs have native carryless multiplication instructions for this arithmetic, while GPUs would need to emulate it. Their parallelism may compensate for that, but only a real implementation and benchmark can answer the question.
The 240 MH/s shown by the GUI is not hardware telemetry and does not detect GPUs. It is an estimate calculated from difficulty and observed block time. Payout addresses also tell us nothing about hardware. One address may represent one CPU, a 200-core server or several machines.
Do you hear yourself? before at fail start chain was at max 10 MH with all those people now it is 300 MH I saw even 400+ at some blocks so before was ok now looks pure GPU