Actually, you are not in software only. There has been a change in Premiere Pro beginning with version 25.2 which depreciated the software-only rendering option. You are actually permanently locked to the CUDA acceleration, not the software-only mode. The software-only mode can no longer be accessed witnin Premiere Pro, and the selection for the renderer now only works if you have a GPU that supports CUDA and a GPU which supports OpenCL installed in the same system. The screenshot that you provided showed the exact rendering mode within the grayed-out window - in this case, CUDA has already been enabled, and you can no longer disable it. The software-only mode could be accessed only in the troubleshooting menu from 25.2 up to and including 25.5 by holding down the Shift key while launching Premiere Pro. But beginning with 25.6, even the software-only rendering option is completely removed (or at least completely relegated to a fallback mode which is activated whenever the GPU's VRAM is depleted), in conjunction with the new requirement of OpenCL 2.0 support now required, resulted in systems running very old GPUs now no longer being able to run Premiere Pro 25.6 or higher properly (in this case, the grayed-out rendering mode window will no longer show anything at all, and you will receive a warning/error message about unsupported GPU hardware and the potential for corrupted renders). And the current point version, 25.6.x, will be the very last version of Premiere Pro (as far as the "Pro" designation is concerned); beginning with the forthcoming version 26, the desktop Premiere app will be renamed to "Premiere for Desktop" (the "Pro" designation will now be applied to the higher-tier Ai-laden version of the Creative Cloud "all apps" subscription (Creative Cloud Pro), with the Ai-light tier now called Creative Cloud Standard). When Premiere for Desktop version 26 hits general release, expect it to be flagged as "Not compatible" if your PC has a very old GPU whose OpenCL support is limited to 1.2 or earlier or nonexistent; in that case, the Creative Cloud desktop app will default the Premiere installation to version 25.1 or whichever point version of 25.x that Adobe deems sutiable for such an old GPU. Currently, Premiere shows up as "Not compatible" if your system is running an outdated operating system (OS) or is equipped with an old CPU which lacks AVX2 hardware support.
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