Adding some Polish Wikipedians who might be able to help efforts to optimize this.

When T349423 is complete and live in production, we'll be able to provide a "proper" solution to this problem for any MW extension or skin using Codex. At that point, a given module will be able to specify a list of codexComponents that it needs and get only the CSS and/or JS files for those components (plus any dependencies).

The installation of ReferenceTooltips for anonymous users by default which loads jquery.ui and oojs-ui-core (perhaps this could be revisited in light of T282999)

The dependency on jquery-ui has been removed from this gadget (it was a leftover from a previous version).

The addition of oojs-ui-core.icons, oojs-ui.styles and oojs-ui.styles.indicator to render blocking CSS (not sure what is adding this but it does not appear to be gadget related and seems related to something on the page calling OutputPage::enableOOUI)

11 OOUI modules (incl. oojs-ui-core.icons, oojs-ui-core.styles, oojs-ui.styles.indicators) are loaded even on an empty page in the safe mode when browsing anonymously - https://pl.wikipedia.org/wiki/Wikipedysta:Msz2001/brudnopis?safemode=1

I used the following to list the modules:

mw.loader.getModuleNames().filter(x => mw.loader.getState(x) == 'ready').filter(x => x.indexOf('oojs') == 0).sort()

I suppose that it might be an issue of DiscussionTools. When running with a clear cache, there are two resource requests that load OOUI:

• https://pl.wikipedia.org/w/load.php?lang=pl&modules=mediawiki.action.view.postEdit%7Cmediawiki.notification%7Coojs-ui.styles.icons-interactions&skin=vector-2022&version=11zo8
• https://pl.wikipedia.org/w/load.php?lang=pl&modules=oojs-ui-widgets%7Coojs-ui-widgets.icons%7Coojs-ui.styles.icons-editing-core&skin=vector-2022&version=4iy6y

The call stack for both looks like (there's only a minor difference in line with controller.js but it doesn't change much for finding the codebase that's loading the libs):

addScript	@	load.php?lang=pl&modules=startup&only=scripts&raw=1&safemode=1&skin=vector-2022:9
doRequest	@	load.php?lang=pl&modules=startup&only=scripts&raw=1&safemode=1&skin=vector-2022:14
batchRequest	@	load.php?lang=pl&modules=startup&only=scripts&raw=1&safemode=1&skin=vector-2022:15
work	@	load.php?lang=pl&modules=startup&only=scripts&raw=1&safemode=1&skin=vector-2022:17
enqueue	@	load.php?lang=pl&modules=startup&only=scripts&raw=1&safemode=1&skin=vector-2022:10
mw.loader.using	@	mediawiki.base.js:793
init	@	overflowMenu.js:8
init	@	controller.js:336
reallyInit	@	dt.init.js:38
mw.dt.init	@	dt.init.js:49
add	@	mediawiki.base.js:495
dt.init.js	@	dt.init.js:77
runScript	@	load.php?lang=pl&modules=startup&only=scripts&raw=1&safemode=1&skin=vector-2022:11
(anonymous)	@	load.php?lang=pl&modules=startup&only=scripts&raw=1&safemode=1&skin=vector-2022:12
flushCssBuffer	@	load.php?lang=pl&modules=startup&only=scripts&raw=1&safemode=1&skin=vector-2022:4
requestAnimationFrame (async)	
... (trimmed but nothing interesting down there)

EDIT: There's a third load (for CSS): https://pl.wikipedia.org/w/load.php?lang=pl&modules=codex-search-styles%7Cext.discussionTools.init.styles%7Cext.uls.interlanguage%7Cext.visualEditor.desktopArticleTarget.noscript%7Cext.wikimediaBadges%7Cmediawiki.widgets.styles%7Coojs-ui-core.icons%2Cstyles%7Coojs-ui.styles.indicators%7Cskins.vector.icons%2Cstyles&only=styles&skin=vector-2022

It originates from the HTML (not surprising, it's styles) but when comparing with analoguous request from enwiki (below) the difference is likely to come from DiscussionTools and its dependencies.

https://en.wikipedia.org/w/load.php?lang=en&modules=codex-search-styles%7Cext.uls.interlanguage%7Cext.visualEditor.desktopArticleTarget.noscript%7Cext.wikimediaBadges%7Cskins.vector.icons%2Cstyles&only=styles&skin=vector-2022

DiscussionTools is loaded on https://pl.wikipedia.org/wiki/Wikipedia:Strona_główna, because it's a page in the "Wikipedia:" (project) namespace. See discussion on T249036: Enable the Reply tool in the Project namespace (Wikipedia:) and other "wgExtraSignatureNamespaces".

That is not ideal for the main page though. The Editing team recently added a way to disable this behavior for individual pages, using the __NOTALK__ magic word (https://www.mediawiki.org/wiki/Help:DiscussionTools/Magic_words_and_markup). I added it to the main page: https://pl.wikipedia.org/w/index.php?title=Wikipedia:Strona_główna&diff=prev&oldid=71731927

That reduced the CSS size from 36.91 kB to 24.14 kB in my testing.

To get comparable results, try comparing pages in the same namespaces and similar content. For example:

Both pages load DiscussionTools (mw.loader.getState('ext.discussionTools.init') === "ready"), and the small increase on pl.wp is due to local styles/gadgets.

Neither page loads DiscussionTools (mw.loader.getState('ext.discussionTools.init') === "registered"). The increase is probably mostly FlaggedRevs? I didn't investigate.