Impossible to avoid the opening of Opera at the Mac's demarrage, even if it is not demanded! Why?

@sgunhouse
Thank you.
I don't think so, but maybe FileMaker could do something of that kind... I always tried to open the document and not the program itself. But I never succeed with the long story of the macs I used... It cannot open itself as demanded. I have to help him to open... If I don't do it, it stay in the middle of the process. I'll try to withdraw FMPro and see if it will be fixed...

@CarlyRaeJepsenStan
No; I didn't...
Thank you!

Opera opens automatically when the mac starts, even if it is not in the list of applications that should open at startup. In spite of all the operations required to prevent it, Opera seems to impose itself against all odds! How to fix it (iMac 27, OS 10.13.6 High Sierra, 3.5 GHz, 16 GB...). Thanks for your advice.