I do not own that particular tv model if thats what You mean so cannot go through it's settings. However right now I'm looking at the HDR10+ webpage on the certified models and right there is the 55Q90R 2019 model, go to www.hdr10+.org and see for yourself.
RTings test page of your model does show that your model does have, in thier words, HFR10+
Under Inputs Specifications.
Chances of Samsung answering your question is probably zilch, but perhaps since you have one of the TV's that RTings has tested, you can contact them and ask them if their tested TV showed ST.2094 under gamma? The website seems like a very serious test lab and maybe they can explain why it's suppose to be HDR10+ but there is no gamma rating that says so. There's even a discussion page.