Slow to respond. The fan is constantly running

See if you can perform the following two tasks to address your concern-

1. Reset SMC How to reset the System Management Controller (SMC) on your Mac - Apple Support If this does not help the perform step 2.
2. Reset NVRAM, PRAM Reset NVRAM or PRAM on your Mac - Apple Support

If none of the above works then have your Macbook examined at an Apple Store.

Axel F.

Read About fans and fan noise in your Apple product. A MacBook Air exhaust fan is in constant rotation unless the Mac is sleeping or shut down.

Please determine if the same problems occur in "Safe Mode": Use safe mode to isolate issues with your Mac.

Another link to article with the word 'fan' inside title and that may offer more clues:

• See how apps affect Mac performance, battery runtime, temperature, and fan activity - Apple Support

https://support.apple.com/en-us/HT203184

Note additional links in above toward bottom of article's contents, with more ideas.