The higher screen resolution is usually better however sometimes if you ended up in the middle range it can make scaling hard as it has to do fractional scaling rather than integer scaling. For example the Macbook's do have higher resolution but that means Ubuntu, etc. can just run at 200% (also known as 2x or integer scaling) so that 3840x2560 resolution is essentially halved to 1920 x 1280 so what you see on the screen "looks like" roughly a 1080p display in terms of the contents size but it is rendered much higher and so the text, screen elements, etc are sharper.
Now Ubuntu (well Gnome, KDE, etc) handle integer scaling just fine so running at 200% is fine. The issues come when you want to run at say 175% or 150%.
That is fractional scaling and is more complex to do well and so on many Linux distros it is disabled by default. Ubuntu does support it but it isn't perfect. You can get some apps that are a "fuzzy" or blurred look to them, especially text
For the processor model, this is hard to give a solid answer on without a bunch of testing on the actual device to know for sure how it handles the heat. Intel have a bit of a tricky history with putting their top end chips (like the Core i9) in a laptop as they just got too damn hot too quickly and would throttle within minutes down to slower than say an i5 or i7 would so while on the spec sheet you have the most powerful chip in the real world when using it you hit the limits of what the laptop can keep cool and you end up with slower performance during prolonged use.
This is sometimes why you see a benchmark of an i5 vs an i9 and the first run the i9 obviously wins by say 5-10% but when the benchmark is repeatedly run for say 30-60 miniutes the times average out and the i5 pulls ahead in performance as the i5 doesnt throttle whereas the i9 does. Not always but has been quite often the case.
Now is it a huge issue? That depends on each user, if you're doing lots of heavy work like editing video or batch processing large photos or gaming for a few hours then yes it may well matter. Just doing office type word, web, etc. you're unlikely to notice any difference. But also that means you've over spent on an i9 in the first place as you wouldnt notice the difference anyway so it is a bit pointless for most people to get the highest performing chip in a thin laptop designed for consumer use
It can be a bit different if you get a "mobile workstation" like a P series ThinkPad as they handle the heat and power of the higher end chips better and so throttle less (if at all)