I'm using muc-off sealant
I think I’ve spotted your issue
Now for some actual advice. One loud pop when seating may not fully set the whole tyre. Keep going until 40-45psi there may well be more to come. Leave wheel to sit 10-15 minutes. If it goes down quickly it’s a sign there’s an air leak. A well taped rim and valve should last a couple of hours without sealant. If it’s going down with sealant added, chances are it’s just not reached the right places yet. Go for a half hour ride even just round town, this spreads the sealant around especially as the carcass flexes. I’ve had tyres go down overnight in the garage on first fitting only to miraculously seal on the first ride.
Also check your valve core is properly tightened.
It’s worth persevering. Slime tubes are no substitute. Heavy and still don’t allow you to run low pressures that tubeless do. Yes, they help with thorns or other sharp punctures but not snakebites. The extra traction and suppleness from a tubeless set up is just superior.