I'm not sure what you're asking here.
Can you hang or cross the roof?
Any creature, with or without climbing speed, can grab onto a roof feature and hang on to it. If the roof is covered with vines, carvings, beams, or has other potential handles, it is up to the DM to determine if the handles can support their weight and what roll (if any) is needed to maintain a grip and / or move through the hand surface on hand.
While most of the climbing rules speak of vertical surfaces, it is quite clear, from our normal understanding of the world, that an action like this would still amount to climbing and would be subject to all the rules related to that. , such as increasing the cost of movement and requiring an athletics run if the surface is challenging. In this case, the speed of ascent works as usual, which allows you to ignore the increase in costs and, potentially, not make runs.
(As examples, I think crossing from something like "monkey bars" on the playground would not require control, or just a minimal CD, while more difficult surfaces, such as a roof covered with vines or move from stalactite to stalactite, they would be much more difficult.)
Can you hang up or climb through a soft Ceiling that lacks handholds or other similar characteristics?
Probably not, unless the source of your ascent rate (or some other rule) specifically says that you can.
For example, him spider rise the spell says
a willing creature you touch gains the ability to move up, down and on vertical surfaces and upside down along roofs
Similarly, the spiders in the Monster Manual share a skill called (again) spider climb, which says:
The spider can scale difficult surfaces, even upside down on ceilings, without the need for a skill test.
The speed of climb of a Simic Hybrid (if I remember correctly) is just an ascent speed that does not include a clause similar to that of a spider, so it would not allow you to cross a roof without something to hold onto.