I recently switched to gmail. Are you within the daily limits? I think it's quite high but there is a limit of 500 recipients for the same email on my plan (the cheapest one).
Also my server AI bot talked me through setting up SPF, DKIM and DMARC as well, but Google itself produced the settings needed to be added - mine is set up in Cloudflare though. The Google info was a bit unintuitive at times. Have you checked in Google Workspace if there is anything remaining to do from their list of recommendations?