Solo parenting a ‘spirited’ child sounds seriously tough.
Have you read any books? If you struggle to find the time listening on audible is a great way.
The Book you wish your parents had read - best one to start with
How to Talk so Little Kids will Listen
Hunt, Gather, Parent
Playful Parenting
For the bath scenario - did you validate or just tell him he had ti and try to explain why. Validating the feelings but holding the boundary on the action can help hugely, plus a bit of silliness.
‘You really don’t want to have a bath. I hear you. You’re very angry at me because I’m saying you need a bath. You never want to have a bath ever again. The problem is [this avoids using but], if you don’t have a bath to clean this mud, your skin will get sore and itchy. Do you want to dive into the bath like a dolphin or hop in like a frog?’
And then if there’s still no cooperation: ‘can you get into the bath by yourself or do I need to lift you in?’
(but no conversation like this until he’s not in meltdown mode, his rational brain won’t be active)
Also worth investing in some bath paints/try a Pom Pom bath/ buy or make bath colourful bombs together
Can he choose bath or shower?
also ‘When, Then’ statements “When you’ve had a bath, then we can play monster trucks/bake a cake etc.