Job Offer Evaluation: €85k Fixed Salary with Benefits and Relocation Assistance

The (PPP) Purchasing Power Parity ratio for the CTC you would be earning of ₹89 LPA in UK is equivalent to ₹31.5 LPA in India. As you’ve already mentioned that your current CTC ₹45 LPA in India, I would advise you to reiterate the negotiation with the HR.
It should be at least 140k£ fixed, if you think I am delusional then no I am not. Don’t be an introvert during negotiations.

For the record, PPP is a worthless argument in most cases.
Especially for UK/Europe, where 140k is highly rare unless you are gunning for leadership roles.

Instead you should do the following

1. You should look at pay for similar roles to gauge if you are getting lower than median pay for the band. You can always ask them to move up towards the higher side of your band.

2. Do an analysis of your expenses, taxes etc. to see “net savings” that you will make.

3. Consider your priorities with work/outside of work

(a) Do you wanna come back to India eventually in a few years or stay & grow there itself. Your savings converted to INR might be still large, but not so high from UK perspective. Consider this.

(b) Are you looking to optimise for priorities outside of work? Such as travelling/having good work-life balance/ learning new skills. These are also benefits that you will get & usually at a lower expense than what you would do from staying in India.

Moving out of the country is a huge move & there is no template. You should also talk to some folks who did similar moves before

It's going to be tight. Also depends on the city / suburb you'll stay in.

Ideally at-least 100K.

42% income tax will leave you with 4K a month. That demands max optimization on lifestyle.

Who did you receive an offer from abroad. Is there any portal?

Just look at the Median pay for that role in that location. Evaluate if it is higher/at par/ lower than that. Given how much risk you are taking, you should aim net net higher than median pay.