You can put what you like in accounts really if protection isn’t an issue.
You can put up to £85,000 in different banks and each bank is protected but be aware of banking groups as I believe you only get protected once per group.
If it’s only 6 months it’s unlikely Monzo will be going bust but you never know.
As @ndrw linked to above, you don’t need to worry about the £85k limit when selling a house as this counts as an event that provides protection of up to £1m for six months.
You get protected per banking licence. Some groups have multiple banking licences, for instance RBS, NatWest, and RBS International operate under difference licences despite being part of the same banking group.
Various easy access accounts listed there, as well as some notice accounts with slightly higher rates.
Like others have said, your FSCS protection is good for up £1m in this situation, so probably no need to split between different accounts.
I don’t think anyone’s said it yet but, when you’re transferring large sums of money around, you should be prepared for banks to ask you a few extra questions about where the money has come from and why you’re moving it, as well as being asked for extra proof of ID. All of which means things may take a bit longer.
One thing to note is that the OP said they’d have the money for ‘about six months’ but the jumbo FSCS protection is only for up to six months. NS&I has full protection for up to £2 million with no time limit.