I have handed my notice in as I returned from maternity leave with my second child, but that may not be a useful or practical solution. So some more practical help:
If you can't sleep train, maximise your sleep by making the nights as easy as possible for yourself. If that means cot/toddler bed in your room, so be it. My vote goes for sleep training once at work because it also helps with daytime sleep in different settings, but every family is different.
Know that now you are working, everything to do with home life should be shared fairly with DH. Housework, night duties, parental responsibilities etc
Try to get some exercise and fresh air
Realise the value and indulgence in going to bed early. Some people stay up late because they prioritise child-free time over sleep. Until night sleep improves, it would be highest priority for me.
Set realistic housework expectations. Similarly as above, place sleep above non-essential housework in terms of priority use of your time.
Practice mildfullness and a lie relaxing even when you don't sleep. Having half an hour in the dark and quiet without looking at a screen or doing anything is valuable even if you don't sleep.
Learn the value of napping in the daytime. Snatch sleep whenever you can at weekends and days off.