Google Scholar indexed journals are absolutely acceptable to me because when doing a systematic review, we use keywords that are suitable for our review procedure. Google Scholar is an academic search platform and its coverage is way wider than other index platforms.
It seems to me that looking at indexes, Scopus journals etc. has become a fetish. The criteria to use or not to use scientific results should be others than just formal ones. One should read critically all papers, whether the journal has a high impact-factor or not. All these formal criteria are just statistical ones. There may be very valuable results also in less known journals, and even high-ranking journals may contain falsified results, as it already happened. The concentration on mainstream science will neglect unusual but creative results and theories.
If you ask any researcher which online outlets they use to find relevant journal articles, there’s a good chance that Google Scholar will be at the top of their list. The 2018 “How Readers Discover Content in Scholarly Publications“ report found that researchers rated academic search engines as “the most important discovery resource when searching for journal articles,” and Google Scholar is among the most widely used free academic search engines available. A 2015 survey on 101 Innovations in Scholarly Communication also found that 92% of academics surveyed used Google Scholar.
With so many researchers using Google Scholar, it’s a search engine that all journal publishers should prioritize. Google Scholar stands apart as one of the most accessible and sophisticated academic search engines available. Inclusion in Google Scholar can help expand the accessibility, reach, and, consequently, the impacts of the articles you publish.
For research outputs, any exposure is good exposure and more exposure is better exposure to disseminate your findings, so I find no reason to avoid having your paper getting published in a Google Scholar-indexed journal. However, you should also consider that not everyone will instinctively go to a single database for their scientific/literature queries, so publishing in a journal that is indexed in not just Google Scholar should be the aim.