Post Brexit (01/Jan/2021) postage issues between EU and UK

From Gov.uk website:
Notice 143: a guide for international post users
(Updated 13 January 2021)
https://www.gov.uk/government/publications/notice-143-a-guide-for-international-post-users/notice-143-a-guide-for-international-post-users

Under international postal agreements, the sender must complete a
customs declaration (form CN22 or CN23), which will be fixed to the
package in most cases. The declaration includes a description of the
goods, their value and if they’re gifts or commercial items.

Most goods arriving in the UK are liable to any or all of the
following taxes:

• Customs Duty
  
• Excise Duty
  
• Import VAT
  These taxes must still be paid if:
  
• you purchase the goods or receive them as a gift
  
• the goods are new or used (including antiques)
  
• the goods are for your private use or for re-sale
  
  

commercial consignments (goods you’ve purchased) of £135 or less are
free from Customs Duty and not subject to Import VAT - this does not
include alcohol, tobacco products, perfume or toilet waters as these
items are excluded from the relief of Customs Duty and VAT at import
is payable

So for private sales under £135, no Customs Duty and no Import VAT.

Which leaves Excise Duty...

Excise duty is applied to try and discourage the use of potentially
harmful products such as tobacco and alcohol. Products that cause
pollution are also singled out for excise duty.
(https://www.thomasnet.com/insights/duty-vs-tariff-what-s-the-difference/)

From Gov.uk website:
UK Trade Tariff: excise duties, reliefs, drawbacks and allowances
https://www.gov.uk/government/publications/uk-trade-tariff-excise-duties-reliefs-drawbacks-and-allowances/uk-trade-tariff-excise-duties-reliefs-drawbacks-and-allowances

This part concentrates on goods liable to Excise Duty. It lists the
rates of Excise Duty chargeable for the following:

• wine and made-wine
  
• beer
  
• cider and perry
  
• spirits
  
• low alcohol beverages
  
• imported composite goods containing alcohol
  
• tobacco products
  
• hydrocarbon oil – this section includes details about rebates for such products
  
• Climate Change Levy
  
• biofuels
  

It appears that bike frames and bike parts in general are therefore not subject to Excise Duty.

So (in theory) whether I put 'Gift' or 'Other', neither should incur any extra charges on a 20 yr old, under-£100 mtb frame.