Is it permissible for me, as a resident in a European country for medical treatment, with an unknown duration of stay, to combine and shorten prayers, and is my prayer at home permissible due to the unavailability of nearby and sufficient mosques?

For a traveler journeying 83 km or more, for a permissible or obedient purpose, it is prescribed to shorten the four-rak'ah prayers and to combine Dhuhr with Asr and Maghrib with Isha, unless they intend to stay for four days or more. It is not permissible to miss congregational prayer except for an excuse, and it is prescribed for the traveler to maintain it. Indeed, some scholars have gone as far as to say it is obligatory upon them if they hear the call, based on the verse: (And when you are among them and lead them in prayer, let a party of them stand with you).