Barring dispensation from the local bishop (e.g., in the current situation of pandemic), Catholics are required to attend Mass every Saturday evening or Sunday and on Holy Days of Obligation, under pain of mortal sin (if one is absent without just cause). Justified absence may include (among other reasons) illness, illness of a family member, being homebound, lack of transport, inability to attend a local mass while traveling, or unavoidable work (e.g. doctors, nurses, LEOs, EMTs, etc.) due to public service or family support obligations.
Canon Law provides for a pastor to dispense an individual from the Obligation "for a just cause and according to the prescripts of the diocesan bishop... or can grant a commutation of the obligation into other pious works."
"When the Mass is being celebrated, the sanctuary is filled with countless angels, who adore the Divine Victim immolated on the altar."
St. John Chrysostom
Introductory Rite