Nearly 4 years in operation, your system may have accumulation of dust, restricting the air flow and in combination with a worn out fan, hence the constant noisy fan. Get a can of compressed air and a soft brush to clean out the system first.  If it can not improve the cooling as before, then you can proceed with the invasive thermal past change.  Follow proper precaution steps while working on the system for a successful maintenance job. 
I have a Inspiron 7786 2-in-1 since 2019.A few weeks ago it started to present fan noisy. With the Speccy app I verified that CPU is reaching sometimes 77ºC, but normally it works between 45ºC to 50ºC, but what irritates me is the constantly noise of the fan. In some videos on YouTube I saw that the thermal paste has to be changed and this abruptly reduces the working temperature and with that the fan is quieter. Is this the case that I change the thermal paste? The specs are: -Operating System Windows 11 Home 64-bit -CPU Intel Core i7 @ 1.80GHz -RAM 32,0GB
Inspiron 7786 2-in-1, fan noise