This is what I could find:
To understand how folate interferes with B12 shots, consider the following points:

Folate and B12 work together in the body for red blood cell formation.
High levels of folate can mask B12 deficiency symptoms.
Excessive folate may lead to neurological damage if B12 deficiency is present.
B12 shots may be less effective if folate levels are elevated.
It's important to monitor both nutrients for optimal health.
Consult a healthcare provider for personalized advice on supplementation.

As for me, I've taken a B-50 for about 40 years and a weekly, sublingual B-12 pill that is to be held under the tongue for 30 seconds while it melts. My bi-annual blood work shows all is in balance with an excess of B-12. Cardiologist approves of the excess because it can make the difference between life and death in case of a heart attack.
Hope you can find something that works for you.