Tentatively, yes, the thumbs up emoji may be increasingly perceived as dismissive or sarcastic. However, much like the original gesture, that usage is dependent on context. At least right now, the thumbs up is often understood as an affirmative in work contexts, even if the perception among younger folk is slowly changing.
The Thumbs Up Gesture Can Be Sarcastic Based on Context
One thing to consider is that the thumbs up emoji formed by analogy to the gesture of giving a thumbs up. Even that gesture (giving a thumbs up) could be construed as approving or acknowledging as well as sarcastic or dismissive depending on context, as this still from a widely-disseminated gif featuring actor Jennifer Lawrence demonstrates:

In the gif (from a 2012 interview), she mouths "Okay" and gives a thumbs up with a non-plussed expression, presumably to something shouted from the crowd. In that example, there is a strong argument that the sarcastic meaning comes more from context than anything else, similar to how "Yes" can be made sarcastic using verbal tone. So context strongly influences the specific meaning of the gesture. (For an academic analysis that determines how the thumbs up is largely positive but dependent on context, see Sherzer, 1991.)
The Thumbs Up Emoji Has Less Context and May Still Be Sarcastic
The emoji may retain that flexibility of use, but its meaning in context can be more difficult to parse because other context cues are absent. There is no vocal tone, facial expression, or other cue if someone only sends ๐. There is only the previous conversation and guesses as to how the previous message could be received. That may make the emoji more prone to change or reinterpretation by audiences.
In a recent NPR story about the thumbs up gesture (Ayesha Rascoe, "The Final Word: Is the Thumbs-Up Emoji Dead?" Weekend Edition Sunday, NPR, 16 October 2022), Susan Herring, a linguistics professor at Indiana University, points out that the connotations of the emoji are fluid and perhaps generational:
I think the battle here is really about the connotations of the emoji, the pragmatic meanings. And those are fluid. [...] It's characteristic of what young people do with language. They're always generating new expressions and new words and new ways of speaking to distinguish themselves in opposition to other groups that are perceived as being out of it or square, as we used to say back in the day.
Roscoe acknowledges both that the articles coming out this week are perhaps clickbait (they're drumming up a big controversy over something minor) and that they are touching a real nerve. Young people may indeed view the emoji as dismissive much more often than other generations, but it has long had potential use for sarcasm (see this Thrillist list from 2016). And it's hardly dead, as Herring and Roscoe both acknowledge. For instance, it still lives in the workplace.
Workplaces Still Commonly Suggest Using the Thumbs Up
As far as what to use, at least at work, the thumbs up emoji is still sometimes recommended. Here is Microsoft's own guide to chat etiquette in the workplace:
Use sentiment and reactions appropriately. The thumbs-up buttonโoften thought of as the โlikeโ buttonโcan help you close the loop on conversations faster, with less back-and-forth. Use it to convey โunderstood,โ โokay,โ or โwill do.โ Use the โlove,โ โlaugh,โ โwow,โ โcry,โ or โmadโ sentiments more sparingly, depending on your teamโs norms.
Acknowledge receipt. Use the thumbs-up or โlikeโ button to let others know that you got or agree with their message.
Harvard Business Review in an article from last May (Tomoko Yokoi, Jennifer Jordan, "Using Emojis to Connect with Your Team") similarly recommends the thumbs up in the workplace as one less likely to offend than more complex and thus fluidly-interpreted emojis:
If you are new or hesitant to using emojis in the workplace, we advise starting with simple emojis (e.g., thumbs up) rather than emojis that represent complex emotions (e.g. laughing emojis with tears) in order to decrease the likelihood that an emoji will offend.
Despite the possible misperceptions of even the thumbs up emoji, it is still an often-recommended tool for use in workplace contexts. View the emoji at work rather like other generational slang; young workers generally adapt to what older colleagues use, even if they sometimes joke about you saying "cool" or "boss" in private. As they learn the workplace context, they'll learn that receiving a thumbs up emoji is okay, until the thumbs up either becomes standardized in their use or they spread a work-sanitized version of their slang.
As for outside work? If you want to avoid the emoji, you may be stuck adding more words (and thus more context) to make sure that your intentions are not missed. But much like the emoji, it will depend on your audience and context whether "Sounds good," "I'll do it," or some other phrase will work.