Well... fetal stem cells are sometimes used for vaccine development... Although they do not actually use any original fetal tissue.

The vaccines do not contain any of the original fetal tissue or cells or cells derived from fetal materials. Although the vaccine materials are purified from cell debris, traces of human DNA fragments remain. The cell lines continue to replicate on their own and no further sources of fetal cells are needed.

Several of the vaccines in use or advanced development for COVID-19 use the cell lines HEK-293 or PER.C6 for production. In other cases, notably the vaccines made by Pfizer, Sputnik-V and Moderna, HEK-293 was used during the testing phase. PER.C6, a retinal cell line that was isolated from an aborted fetus in 1985 was used by Janssen in development of COVID-19 Vaccine.
https://en.wikipedia.org/wiki/Use_of_fetal_tissue_in_vaccine_development

So the original cells may have been harvested in say 1985 from fetal tissue, but the cells actually used for research in 2019/2020 were lab grown well after that. No different than studying any other cell line, you have to grow enough to be able to work with it. Certain cell lines are more useful for research than others because of certain genetic differences.

And that ignores the Catholic Church's official stance...

The Catholic Church is opposed to abortion. Nevertheless, the Pontifical Academy for Life, concluded in 2005 that parents may allow their children to receive vaccines made from fetal tissue if no alternative exists and there is a grave health risk.

On December 21, 2020, the Vatican's doctrinal office, the Congregation for the Doctrine of the Faith, further clarified that it is "morally licit" for Catholics to receive vaccines derived from fetal cell lines or in which such lines were used in testing or development, including the COVID-19 vaccines, because "passive material cooperation in the procured abortion from which these cell lines originate is, on the part of those making use of the resulting vaccines, remote. The moral duty to avoid such passive material cooperation is not obligatory if there is a grave danger," such as during the COVID-19 pandemic, and that "in such a case, all vaccinations recognized as clinically safe and effective can be used in good conscience" and "does not and should not in any way imply that there is a moral endorsement of the use of cell lines proceeding from aborted fetuses".

https://press.vatican.va/content/salastampa/en/bollettino/pubblico/2020/12/21/201221c.html

So these self-proclaimed Catholics aren't even following what their Church says.