help with kernel task, tried everything

This is a long story.

I have a MacBook Air 13 “ early 2015

I’ve had it since 2017 and it’s very well cared for.

Around the time I installed the last Catalina update it started being slow, beachballing and it ended up being unusable.

This is what I’ve done so far:

• backed up and reinstalled macOS
• moved all my documents to an external hard drive
• ran diagnostics: no issues found
• ran first aid on all disks
• joined macOS beta and installed big sur - it kept happening so I left beta and installed Catalina again.
• purchased etrecheck - no issues apart from kernel task using up too much CPU - realised that’s the issue.
• purchased clean my Mac and ran the tasks - improvement shown.

current situation: my MacBook is perfect every other day. It goes from amazing to unusable in minutes. Right now I finished running first aid again. Now it works. I just don’t think it’s normal to have to run first aid on recovery mode every day.

kernel task keeps using up CPU randomly, even when no apps are open. I noticed finder crashes often so I reLaunch it also often.

I read a lot of entries here about kernel_task and some solutions, such as disabling display effects. I just don’t think it’s ok to have a MacBook and have to use it partially because of this.

someone suggested that maybe the fans are dusty. If that was the case, wouldn’t the MacBook be always slow and hot, and not only random days?

can anyone provide some guidance on what to do?

there is no Apple store in Malta, there is an iCentre but I don’t trust a shop that sells cheap accessories probably bought on eBay and that give out nivea cream. They don’t have a Genius Bar and Apple products are more expensive than in a real Apple store. So I can’t take my Mac there.