There definitely are some valid reasons why pages built on Bubble may be less than optimal in the ‘Technical SEO’ department (mostly to do with page-load speed and lighthouse scores etc. - most of which is out of the hands of a Bubble developer, and tied to how Bubble apps work and what they technically are).
That said, technical/on-page SEO is only one part of an effective overall SEO strategy and, in my personal experience, the aspects of technical and on-page SEO which Bubble performs badly in are fairly insignificant in real-terms, as long as the on-page/technical SEO aspects that you can control (which to be fair is most of them) are configured correctly, and follow best practices. When doing so there’s no reason you can’t rank Bubble app pages highly on Google (providing you have a solid and consistent off-page SEO strategy).
I currently have multiple pages, from several different Bubble apps, ranking on Google on page 1 (including in the number one spot, and featured snippets) for relatively high competition keywords in various niches.
And although I suspect that the technical limitations of Bubble may be a slight hinderance, if your off-page SEO is on point, and other SEO strategies are up together, based on my personal experience, it’s not particularly significant.
My personal opinion is that those saying Bubble is inherently bad for SEO probably don’t know very much about SEO (given that, there are really only a few, relatively minor factors of SEO that Bubble falls short on, and those don’t, at least in my experience, seem to be that significant in actually ranking pages, if you know what you’re doing).
That’s not to say, that Bubble doesn’t have some deficiencies, compared to other solutions, but I think the significance of those is often overstated.
One day I plan to conduct a side-by-side SEO test of a page built on Bubble compared to a page not built on Bubble (in as objective a way as is reasonably possible). My suspicion is that the non-Bubble page will perform slightly better, but I don’t expect it will be a huge difference.
In my personal opinion, of all the reasons to avoid using Bubble (and there are some legitimate reasons), SEO is not a major one.