Most complex and good looking Ui’s are made with photoshop. I wouldnt recommend making Ui’s with roblox studio’s tools because it isnt as reliable. If you cant afford Photoshop you can make Ui with sofware that is meant for it or you can just go for paint dot net.
I don’t recommend either Photoshop or Photopea, try something like Figma or Lunacy.
Photoshop and Photopea are more designed for raster graphics, Figma is really good for making UI and vector graphics. (to make drop shadows in Figma, just select a Frame and add an effect, it’ll automatically add a 4px width and 4px height drop shadow)
And also @Acvious UI designing in PDN is a really bad idea, just because it’s hard to select stuff after you’ve placed it, and as far as I’m aware, you can’t modify rounded corners that much.
Not sure if this has already been said, but I actually use a free Adobe Software called ‘Adobe Xd’ or ‘Adobe Experience Design’. It’s free for one user (meaning you can’t collaborate with other people on the same file, but I don’t see that as a necessity) and overall a great software. It comes with great colour tools and the ability to add plugins. However, to access it you need to download the Adobe Creative Cloud here.
If you don’t feel like downloading a piece of software, you can try using Figma which is a totally free online software very similar to Adobe Xd.