Exactly, all of the factors mentioned could be involved, but deep-sea methane emissions are unlikely:

Greenland ice: the IPCC predicts that if the atmosphere warms by 3°C to 5°C, an almost complete melting of the Greenland ice sheet and the West Arctic ice sheet can be expected irrevocably over several millennia. 9.4.1 (correct)

Permafrost emissions: According to the IPCC, the permafrost soils of the Arctic and boreal regions store almost twice as much CO₂ as the current atmosphere. Therefore, the permafrost regions that are currently thawing are, with medium probability, net_{CO2 and} CH₄ emitters (IPCC 2021 p. 188) (correct)

Deep-sea methane emissions: Ocean sediments store the majority of the world's clathrate (methane hydrate) reservoir. However, the increased release of methane from these hydrates is very unlikely despite rising water temperatures. This assumption is consistent with the overall low releases of methane during the last deglacial transition despite the major climatic restructuring. Due to the long time associated with the destabilisation of clathrates, it is unlikely that the release of methane from the ocean will change significantly. (IPCC p. 740) (wrong?)

Dieback of rainforests: The IPCC notes that drier conditions, increased fires, and deforestation may combine to push rainforests past a tipping point that leads to significant ecosystem change. The land surface would rapidly degrade, moisture recovery from the atmosphere would decrease, while rainfall runoff would increase and a shift towards a drier climate would occur. (IPCC p.1149) (low probability) Tropical Forest (5.4.8; 8.6.2) (correct)

Source:

IPCC. (2021). Climate Change 2021 The Physical Science Basis WGI. In Bulletin of the Chinese Academy of Sciences (Vol. 34, No. 2).