If its there, and this is first time hearing about it for me and seemingly for others, please provide some serious proofs for such serious accusations.
For example, "Also, they could just remind people that China released COVID which killed millions and cost countries billions." (which, well, those are definitely words.)
China is ... complex. But you seem to be consistently pushing a specific agenda in the way you choose to address it. Why?
I wonder if any anti-Japanese sentiment has to do with the fact that, to this day, the ruling party/LDP actively denies the numerous war crimes perpetrated against the Chinese in the second world war, including the Nanjing massacre. But I guess it must be all that propaganda. Though the Chinese may need to fine-tune their approach, since per the Newsweek article you linked "Among Japanese respondents, 92.2 percent had an unfavorable opinion of China, up from 87.3 percent in 2022. On the Chinese side, 62.9 percent viewed Japan negatively, about the same as the previous year."
75% of the comment is just things that happened, so there's nothing to "believe" there. For the rest it's basically two statements:
1. Ultra-nationalism is on the rise in China
2. Going to China as an outsider is ill-advised
OK so #1 may or may not be true but either way is an objective thing, it's either rising or it's not. So again, not really anything to be "believed," although you could certainly think it's moving one direction and just be wrong about it.
So the charitable reading of the only remaining statement is essentially "you probably shouldn't go to China if you're a foreigner" which yeah is an opinion, and not one I'd take particularly seriously, but it's also not outlandish that someone would believe that. There are plenty of places in the world to visit and if there's a place with a higher chance the locals don't actually want me there, I'll go elsewhere.
Most of the time when I see questions like this asking if someone "actually" believes something, the implied second part of the question is either "or are you a troll" or "because no rational person could possibly believe that," neither of which seem appropriate in this instance.
1. You are fluent in the langauge. 2. While acquiring fluency, you learn the culture. 3. You will be able to hold your own w/o a local interperter. 4. You can change locals mind and let them see their news/version of events isn't all secular (e.g. laowai adapts culture, learns langauge, not to fit in, but complimentary to living/being in China, etc.)
So, I would say for someone that is fluent, it is the best time to go.
General tourism, business investment, FDI, etc I'd say yes don't be too special. Note that the links you used really reference tourists.
Investment into China by foreign businesses slumped to a 30-year low in 2023 https://qz.com/china-foreign-investment-30-year-low-18512681...
Number of foreign visitors to China in 2023 down more than 60% from pre-pandemic levels https://www.cnn.com/travel/china-foreign-visitor-number-2023...
Remember that as the Chinese economy worsens, the average citizens are going to convert their anger into violence against foreigners.