Massive shift in gamma/brightness when rendering proxies

I am working on footage shot on a sony a7 III. The codec is XAVC-S 50p HD 50mbit. It was shot in HLG3 for wider dynamic range but the output is SDR not HDR. As HLG3 is detected as HDR in final cut, I am using the setting "color space override" and set it to Rec. 709 - as this is my final output. The Library is set to Standard Gamut (NOT Wide Gamut HDR) and the Timeline is set to Rec 709 as well. This has been working so far, as I basically have footage similar to Rec. 709 and can recover highlights if necessary. But now I tried to render proxies in H264 very low quality for all my footage (drone shots in highres etc...) to be able to edit on the go. In the proxies the drone footage looks fine, some XAVS-S footage from the sony as well - which was shot in cine4 (a SDR-profile), BUT the HLG3 footage is WAY too bright. Here are two scopes of the same image on the timeline - one for the original footage, one for the proxies. Is there a way to get it right? I guess, only prores could maybe help..

I tried to render proxies in prores - still the same.