Is there a risk to damage the thunderbolt port?
No. It's a "smart connector" and will only try and charge the computer if the computer asks for it.
And would this monitor 4K give sharp text at a 2560x1440 resolution?
NB: I'm going to assume you. meant U3223 - which would be a 32" display and not U2723 which would be 27". If there really
is a 23" version I'll be right out
Can't speak for that particular display - but for a 4k, 16:9 display in general:
(NB: One day I'll have a version of this spiel with which I'm happy so I can just link to it... so don't worry too much if it's TLDNR. Trouble is, complicated subject is complicated...)
MacOS will choose a default "best for display mode" (probable "1920x1080") but if you go into Display Settings and click on "Scaled" you'll get a choice of alternatives. It's important to understand that the "resolution" figures you see in "Display Settings" for a 4k or better display aren't really the "resolution" and don't have the same meaning as they would for an old-school low res display. Unless you jump through hoops to get the advanced choices
all the modes will put the display itself into native 3840x2160 and
none of them will give the same horrible mush that you'd get running a lower-resolution display in anything other than native mode.
"1920x1080" actually means "3840x2160" (native) but with a double-sized User Interface (a.k.a. HiDPI mode) - that is to say the system fonts, icons, menus, window furniture, default window sizes etc. will be displayed at double size (and application zoom/page size settings interpreted accordingly). Everything will be perfectly sharp and detailed, using full 4k resolution (apart from a few very old, pre-retina-display apps, which may look fuzzy)
but those icons and menus will be a bit on the large side on a 32" screen.
"3840x2160" - on the other end of the scale - is the same, native, resolutions but without the HiDPI mode. This should be quite usable
on a 32" display if your eyeballs are a few decades younger than mine - but it's certainly too small and fiddly for most on a 27" display. I can just about cope with it for short periods on a 28" display.
Note that - although you'll find them under "Scaled" in the dialog, the two modes above are
not the dreaded "(fractional) Scaled modes". Those are:
"2560x1440" which is actually done by creating a virtual "5120x2880" screen (in HiDPI mode) - i.e. 5k - which then gets downsampled to the display's native 3840x2160. The result is that - on a 27" display - you would get the same physical "UI size" as the default on a 27" iMac - and with far more detail than you'd get on an old school, non-retina 1440p display. The UI size is still probably a bit big for a 32" display - so there are "3008x1692" and "3360x1890" modes that give you progressively smaller UI sizes and may be better on a 32" display.
There are 2 "problems" with these modes. First, as Apple will warn you if you select them, "Using a scaled mode may affect performance" - and they do put an extra load on the GPU. However, you get the same warning on a 10-year-old MacBook air with Intel integrated graphics - I don't think the M1 Max is going to break a sweat.
Second, because 1 pixel in the "virtual screen" no longer corresponds to an exact number of pixels on the physical screen, everything has a slightly "soft focus" look and if you drag something slowly, pixel by pixel it will move slightly unevenly, or "shimmer".
Opinion seems divided on whether that is completely irrelevant unless you habitually climb up on your desk with a jeweller's loupe and do endless A/B comparisons with a Pro XDR display - or if it is completely unusable, will make your eyeballs bleed and your hair fall out. Ultimately, I tend towards the first point of view, but your mileage may vary, especially if you habitually lean in to the screen while trying to make pixel-perfect adjustments to graphics. It
will be more noticeable if you have a 32" display but don't compensate by moving it further away.
...but, of course, you can always put up with the slightly big icons and dialogs in "1920x1080" mode and just set the zoom/scale/font size in your App to "actual pixels" or whatever - especially if you auto-hide the dock and menu bar, or work in full screen mode -and there's no standard for how big/small toolbars etc. are in third party apps.
Ultimately, yes, MacOS is optimised for ~220ppi, which means 5k@27" and 6k@32" and you'll get the best results with a Studio Display or Pro Display XDR... at $1600 or $5000 respectively (plus extra for a decent stand)... However, 4k displays are a perfectly good compromise for many people's needs. If your main requirement is lots of screen estate for code, spreadsheets etc. then you can get
multiple 4k displays for the price of a single 5k/6k one.
