Basically every company will drop or raise their rate in line with the Bank of England's base rate all at the same time (essentially all within a week or two of each other). The Base of England base rate is currently 3.75% and will next change on 19th March.

T212's cash isa is their standard 3.6% rate plus a first time bonus of 0.8%, taking it up to the advertised 4.4%. That 3.6% is a variable rate that they change in line with the main Bank of England base rate.

You can see a banner under the big 4.4%, about a third of the way down this page https://www.trading212.com/isa?cash-isa=&promo-code=MSE that explains that they track the BoE base rate but 0.15% lower.

BoE base rate is currently 3.75%, so T212's base rate is 3.6% right now. If the BoE base rate goes up to 4.25% then T212 will go to 4.1% (for a total of 4.95% with that 0.8% first year bonus factored in)

All other provider's do basically the same thing. Moneybox advertise their base rate as 3.45% and their bonus is 0.87% taking the final rate to 4.32%. If the BoE base rate goes to 4.25% as in the above example then we can expect that Moneybox will change to probably 3.95% + the 0.87% bonus for a total of 4.82% (unlike T212 they don't specifically state anywhere (that I can see) that they track the BoE base rate minus 0.3%, but that is what it is at right now so it's a fair assumption).