CleanmyMac

No, CleanMyMac can do more harm than good.

3rd party Anti-Virus software is not necessary for your Mac, and can damage data on your system. macOS has it's own malware protection software included.

Same goes for 3rd party programs that claim to "optimize" your Mac.

Check this discussion about it:

Is Norton 360 necessary if I run ClearMyM… - Apple Community

I would not trust any "trusted friend" if they recommend using completely pointless software which can seriously bork your system while trying to access it within the read only and inaccessible volume which is where it was put by Apple for security purposes.

PatsyGra wrote:

Does Apple recommend it?

Apple doesn't recommend it. And, the vast majority of experienced people on this forum actively recommend against it.

along with the good advice from Ingo2711, (which I second) please see this informative user tip: Effective defenses against malware and other threats - Apple Community. it's a long article, but it's worth your time to read every word.

you're welcome. :) and,

PatsyGra wrote:

For a start I got rid of Adobe flash player. Is there an alternative for Mac?

to the best of my knowledge, flash was replaced with HTML5. there is nothing new that you need to install.

No problem!