The government have been asleep on the job as regards opining on the giving of tax advice to Russians who are not directly on any sanctions list. I note from the Chartered Institute of Taxation’s guidance that they ask to be informed if a firm regulated by them carries out tax work for Russian clients. There appears to be no explicit blanket ban on giving tax advice to Russians, or persons connected with them. The CIoT guidance can be found here: https://www.tax.org.uk/new-financial-sanctions-in-relation-to-russia
Cyprus international trusts should not, in principle, cause undue suspicion or caution (although it is well known that Russians have made frequent use of them). They are statutory trusts and the legislation is based essentially on English trust law. As Cyprus has extensive anti-money laundering/terrorist finance legislation as one would expect from an EU member state, in principle, one would expect that the Cypriot trustees (many of which will be well known to offshore trust practitioners) will have carried out all due diligence. In these circumstances, I would almost certainly ask to be instructed by the Cypriot trustees rather than by the settlor or anyone connected with him/her or by a beneficiary.