As you need 25% of your equity ISA in cash within the next six months, then personally I would be selling things to cover that cash. Assuming you can't borrow it from somewhere, ie mortgage or personal loan.
You might be able to slightly reduce that amount if you are expecting dividends but even that is not guaranteed.
To me, there is so much downside risk, remember covid, shares tanking and divis cut etc. Ukraine, strikes, black Swan or Monday. Mr Market has been on a run this year and I expect him to take a breath at some point.
There is also the risk of what would happen if you don't have the funds available at the six months point. Could you end up homeless or just loose a house move that you are set on. The emotional costs might be worse than the financial ones.
The Ftse is on a high, great if you need to sell. Could if rise further, maybe but how much further and what are you likely to gain. Another 10% rise gets you just 2.5% of what you need. Unfortunately I expect that over the next six months there will be a dip in the market and generally the dips tend to be short and sharp. I donk know how you would behave in those circumstances with your current issue.
So in my view the risk v reward is highly geared towards sell now and deal with the known about having cash in the bank or banks possibility if its over the £85k guarantee.
Good luck with your decision. You will be able to look back in 7 months time with hindsight at what he best course of action was and also the worst one.
Lucky dip ticket?