It will be solvent weld or at least it should be. Certainly the end that joins to your stack will be, the other end might be ring seal.
The fitting you require is called a ‘Boss Adaptor’
Being honest, for wetrooms I’d go for 50mm solvent weld waste right up as close to the wet room drain as possible.
With boss adaptors they are manufacture specific so you need to find the brand of ‘boss coupling’ that you have to know which boss adaptor you require.
I can’t think for the life of me which brand of fitting that is you have. Worse case scenario replace the Boss coupling. Simple job really.