If by high school you mean lukio/gymnasium, the Finnish info is available in Finnish and Sápmi https://www.oph.fi/saadokset_ja_ohjeet/opetussuunnitelmien_ja_tutkintojen_perusteet/lukiokoulutus and in Swedish at https://www.oph.fi/lagar_och_anvisningar/laroplans-_och_examensgrunder/gymnasiet .
The English version does not seem to be free, but does seem to be available, supposing by "high school" you mean upper secondary education: https://www.oph.fi/english/curricula_and_qualifications/general_upper_secondary_education .
In case of link rot, one should search the webpages of Opetushallinto/Utbildningsstyrelsen, the Finnish national agency of education, for more topical links.
If one wishes to read the official document via machine translation, I would recommend starting with the Swedish document as the baseline. Swedish is a larger language and an Indo-European one, so machine translation to other Indo-European languages is likely to be of higher quality, and the document by itself is also easier to understand for someone who knows Indo-European languages. (Use Finnish if machine translating to e.g. Estonian and maybe Hungarian.)
Structure and role of lukio/gymnasium studies
After compulsory education, a child may go to lukio for general studies or to ammattiopisto/yrkeskola to qualify for a profession. Both lukio and ammattiopisto qualify one for higher vocational studies (bachelor level) and lukio also prepares one for university studies (typical default is master level).
In lukio one has to take a certain amount of courses, in addition to which there is the national matriculation examination. Some courses are compulsory. One can take either "short" or "long" mathematics studies, with different compulsory courses. It is possible to change from one to the other during studies.
Books in mathematics for lukio/gymnasium, in Finnish
There are Finnish books in natural science available here: https://www.akateeminen.com/kirjavalikoima/oppikirjat/lukiokirjat/matematiikka . Matematiikka is mathematics, pitkä means long, lyhyt means short.
(Biologia is biology, fysiikka is physics, kemia is chemistry.)
Books in short mathematics: https://tuotteet.sanomapro.fi/tuotteet/lukio/lyhyt-matematiikka.html
Books in long mathematics: https://tuotteet.sanomapro.fi/tuotteet/lukio/pitka-matematiikka.html
Books in both mathematics: https://otava.kauppakv.fi/sivu/lukio-matematiikka/
Mostly books in lukio mathematics: https://www.huuto.net/osasto/kirjat-ja-lehdet/lukion-oppikirjat/matematiikka/285 (this is an Ebay-like site.)
A couple of open textbooks of unknown quality: https://avoinoppikirja.fi/mat-lukio