For over a year now, I use a Raspberry Pi 4 (with 8GB of RAM) as my daily desktop computer. I browse the internet, read and send e-mails, program software, edit photos, create images, watch Youtube videos and play games on it. Without any significant problems.

Why should you do this? RPis are single board computers, and although you can run a desktop OS on it, they seem better suited for other purposes?
Because I was done with the fan noise of my older and more powerful computer. After a while it felt as if a fighter jet was taking off next to me, constantly. I moved my old computer more away from me, but that wasn't enough. I needed to change something, newer computers were way too expensive for me, and I already had the most powerful RPi laying around. It was time to see if this made a difference and if my RPi was a workable solution.

And then? What did you do?
I tried different OSes, all Linux based, and eventually installed Ubuntu Mate on it. Regular Ubuntu was not snappy enough, even the mouse cursor had just enough lag to become annoying. I also tried Raspberry Pi OS, and although it was usually snappy, I missed some key features like Redshift (to reduce the blue glow from my screen) and some other ones. I was also used to have some kind of dark mode for my OS, and Raspberry Pi OS didn't provide that. Xubuntu was perfect for my old laptop, but I had trouble installing it on the Pi. It required an install of Ubuntu Server and separately an install of Xubuntu Desktop. It took ages to install and it didn't work out. I briefly considered trying Manjaro, but I never tried it. I had already decided to stick with Ubuntu-based stuff, just to have the same kind of workflow I was used to. So I can't comment on Manjaro.

So Ubuntu Mate it is. Did you install the latest version, Jammy Jellyfish (version 22.04)?
Yes, I did. But it was too slow for my liking, and probably too heavy for the RPi. So I went back some versions and opted for Focal Fossa (version 20.04). I'm just more of a cat person, I guess.

Now I'm also considering an RPi with Ubuntu Mate. What do you use it for? Can I play games on it as well?
I mainly use it for browsing (Firefox), creating documents (LibreOffice), edit images (GIMP), edit short videos (KdenLive), programming (Pluma as my text editor and LAMP stack for running a localhost), and some simple games like Mahjong and Solitaire. Unfortunately, I wasn't able to get SuperTuxKart running (which did run very well on Raspberry Pi OS, for that matter). If you are a heavy gamer and like to run visually heavy games, don't use a RPi, but you probably knew that already.

But doesn't your RPi get hot? And don't you need a fan to keep temperature at bay?
The passive cooling block that I use is made of aluminum and doesn't have a fan. It keeps the RPi cool enough. I also installed Psensor to keep an eye on the temp and give me a warning if it gets above a certain threshold that I configured. Only while watching videos on Youtube I sometimes get a warning, but the RPi keeps running.

Conclusion
There it is on my desk, a card-sized computer that I don't hear. Running smoothly for over a year now, providing me with my daily computer needs. I use a big USB stick as my hard drive and I attached a physical on/off switch for the power supply. I had it running from a powerbank for a while and in the future I want to see if I can make this a mobile setup, together with a self built case and a touch screen from Waveshare. Like a fat and heavy tablet computer (or a cyberdeck). Running Linux instead of iOS or Android, how cool is that!?