In reply to obi-wan nick b:
What type of riding do you think you would start with, and what might be the hardest you would aim to do? Where and on what type of trails would it be?
Above a certain price point it’s hard to get a bad bike nowadays, but some might be a bit less suitable for you depending on the answers to the above. Certainly if your last riding was 15 yrs ago, bikes will feel a lot more capable, and the amount of travel will do far more than the numerically same back then.
Don’t get too hung up on “modern” geometry, and higher levels of components, unless you’re a very discriminating or experienced rider, you probably won’t notice much difference. But very roughly, a “slacker” bike will feel more secure on the downs, but harder work on the ups.
Try to have a good test of how a bike feels. Sizing and geometry varies between brands.
A good starting point would be a full suspension bike with 110-140 travel front and back, across the XC to trail categories, or the new modish “down country” in between category.
(I love my Scott Spark 2022, as a single quiver bike that is fast and efficient on ups and flats, and that can still get me down easier black runs with the sort of drops and gap jumps that middle age timidity is ever likely to allow me to do!)