Laptop freezes after a while.

I recently received a laptop (through work) that I would like to use. Normally I assemble old laptops for giveaway to people with little to spend, but I would like to keep this one. The reason I want to use this laptop is that it is the only one capable of connecting via Thunderbolt. I have an external GPU that I would like to use with it.

Unfortunately, after installing Windows 10, the system consistently freezes spontaneously. It becomes completely unresponsive. If I restart it, the issue occurs even more quickly. (So, I thought, maybe it's related to heat.) Since it's an older laptop, I considered that the thermal paste might be deteriorated. Upon inspection, I found that indeed it wasn't in good condition (dry and crumbly). I replaced the thermal paste, but unfortunately, that didn't resolve the issue.

I tried swapping out the memory and the hard drive, updated SupportAssist/drivers and Windows, and disabled certain features in the BIOS (such as Thunderbolt, etc.).

I have no idea what else I could try.

Does anyone have any good ideas?