Breakjan, it's always good to see a new, enthusiastic editor join Wikipedia. However, it is better not to tackle some of the Wikipedia processes until you gain more experience with editing on the site and how things work. That is true for the GA process, where we always recommend that editors have experience with editing articles and improving their quality prior to getting involved with judging higher-quality articles.
A great deal should go into a GA review. In addition to reading through the article and checking for grammatical issues, and that the prose is clear and concise, there are structural issues that need to be checked including certain Manual of Style criteria listed under the GA criteria: one thing that both articles currently violate is MOS:LEAD, for example.
I see that you have already reversed your passage of Singaporeans; it needs a great deal more in terms of in-line source citations before it can meet the verifiability criteria. There are also gaps in the coverage; for example, the Orang Laut are mentioned as the original inhabitants at the time the English made Singapore an open port in 1819, but the second paragraph under Indigenous populations contradicts itself regarding the numbers, and the final sentence is unsourced. There's also a mention of the Dutch with no explanation of why this is relevant.
There are also some problems with Jewel Changi Airport. While it is more thoroughly sourced, much of the sourcing is future based: of restaurants that were announced as going to be opening in the future, rather than that the restaurants had actually opened and/or are currently doing business at the airport—not all announced or scheduled activity actually come to pass. There's also some problematic wording, notably in the Retail section (brands are not duplex stores, and "unique" is a "peacock" term that shouldn't be used), and inconsistent spelling ("meter" vs. "metre"), all of which should be flagged in a thorough review.
Another thing a GA reviewer needs to do is check the given sources to make sure that they support the text while at the same time there isn't any copying or close paraphrasing from sources. It doesn't seem feasible that you did those necessary checks in the time you spent on those reviews today.
Under the circumstances, I will be reversing your passage of Jewel Changi Airport; the article, as it stands, does not yet meet the GA criteria. I hope you will wait to gain more experience as a Wikipedia editor before attempting any further GA reviews. Best of luck in working on articles here at Wikipedia! BlueMoonset (talk) 22:56, 14 February 2020 (UTC)
You are suspected of sock puppetry, which means that someone suspects you of using multiple Wikipedia accounts. Thank you. ——SN54129 20:36, 19 February 2020 (UTC)