There are some misconceptions about how much is too much. Here are some studies with high dosing and no side effects. It's actually exceedingly rare to actually take too much, but it can happen.
This study shows that Vitamin D3 is very effective against Covid (60,000 IU's for 7 days).
Short term, high-dose vitamin D supplementation for COVID-19 disease: a randomised, placebo-controlled, study (SHADE study)
"10 (62.5%) participants in the intervention group and 5 (20.8%) participants in the control arm (p<0.018) became SARS-CoV-2 RNA negative. Fibrinogen levels significantly decreased with cholecalciferol supplementation (intergroup difference 0.70 ng/ml; P=0.007) unlike other inflammatory biomarkers."
This study is about Vitamin D3 and it's effect on psoriasis(dosing levels).
Daily oral dosing of vitamin D3 using 5000 TO 50,000 international units a day in long-term hospitalized patients: Insights from a seven year experience - PubMed
"In summary, long-term supplementation with vitamin D3 in doses ranging from 5000 to 50,000 IUs/day appears to be safe."
On a personal note, I'm at the very bottom of this range (5,000 IU's daily).
This is for critically ill people with extremely low D3 levels.
Short-term effects of high-dose oral vitamin D3 in critically ill vitamin D deficient patients: a randomized, double-blind, placebo-controlled pilot study - PubMed
"This pilot study shows that a single oral ultra-high dose of cholecalciferol (540,000 IU) corrects vitamin D deficiency within 2 days in most patients without causing adverse effects like hypercalcemia or hypercalciuria."