Is refraining from going to the mosque due to fear of harming the mosque or the worshippers by involuntarily passing stool or urine considered a sound decision Islamically, and does it align with the concession granted to one who has eaten garlic, and does the Hadith, "Indeed, Allah loves for His concessions to be availed of, just as He dislikes for His disobedience to be committed," apply to it?

If what you feel is merely fear and a whisper [from Satan], then it is not permissible for you to stay away from the mosque. However, if it is confirmed or you strongly suspect that some urine or feces will fall onto the mosque's carpet, then you are permitted to stay away from it. In fact, it is forbidden for you to enter it, to prevent harming Muslims and polluting the mosque. You will be rewarded for your sincere intention to attend the congregational prayer as if you had attended it. As for the hadith, "Indeed, Allah Almighty loves for His concessions to be availed," it does not apply to your situation, because either it prevents you from entering the mosque due to polluting it, or you have no excuse to stay away if you do not fear polluting it.